Photomask blank and photomask

ABSTRACT

A photomask blank is provided comprising an etch stop film which is disposed on a transparent substrate and is resistant to fluorine dry etching and removable by chlorine dry etching, a light-shielding film disposed on the etch stop film and including at least one layer composed of a transition metal/silicon material, and an antireflective film disposed on the light-shielding film. When the light-shielding film is dry etched to form a pattern, pattern size variation arising from pattern density dependency is reduced, so that a photomask is produced at a high accuracy.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a Divisional of application Ser. No. 11/715,346,filed on Mar. 8, 2007 now U.S. Pat. No. 7,767,366, the entire contentsof which are hereby incorporated by reference and for which priority isclaimed under 35 U.S.C. §120.

Application Ser. No. 11/715,346 claims priority under 35 U.S.C. §119(a)on Patent Application No. 2006-065800 filed in Japan on Mar. 10, 2006,the entire contents of which are hereby incorporated by reference.

TECHNICAL FIELD

This invention relates to photomask blanks from which are producedphotomasks for use in the microfabrication of semiconductor integratedcircuits, charge coupled devices (CCD), liquid crystal display (LCD)color filters, magnetic heads or the like, and photomasks producedtherefrom.

BACKGROUND ART

In the recent semiconductor processing technology, a challenge to higherintegration of large-scale integrated circuits places an increasingdemand for miniaturization of circuit patterns. There are increasingdemands for further reduction in size of circuit-constructing wiringpatterns and for miniaturization of contact hole patterns forcell-constructing inter-layer connections. As a consequence, in themanufacture of circuit pattern-written photomasks for use in thephotolithography of forming such wiring patterns and contact holepatterns, a technique capable of accurately writing finer circuitpatterns is needed to meet the miniaturization demand.

In order to form a higher accuracy photomask pattern on a photomasksubstrate, it is of first priority to form a high accuracy resistpattern on a photomask blank. Since the photolithography carries outreduction projection in actually processing semiconductor substrates,the photomask pattern has a size of about 4 times the actually necessarypattern size, but an accuracy which is not loosened accordingly. Thephotomask serving as an original is rather required to have an accuracywhich is higher than the pattern accuracy following exposure.

Further, in the currently prevailing lithography, a circuit pattern tobe written has a size far smaller than the wavelength of light used. Ifa photomask pattern which is a mere 4-time magnification of the circuitfeature is used, a faithful shape corresponding to the photomask patternis not transferred to the resist film due to influences such as opticalinterference occurring in the actual photolithography operation. Tomitigate these influences, in some cases, the photomask pattern must bedesigned to a shape which is more complex than the actual circuitpattern, i.e., a shape to which the so-called optical proximitycorrection (OPC) is applied. Then, at the present, the lithographytechnology for obtaining photomask patterns also requires a higheraccuracy processing method. The lithographic performance is sometimesrepresented by a maximum resolution. As to the resolution limit, thelithography involved in the photomask processing step is required tohave a maximum resolution accuracy which is equal to or greater than theresolution limit necessary for the photolithography used in asemiconductor processing step using a photomask.

A photomask pattern is generally formed by forming a photoresist film ona photomask blank having a light-shielding film on a transparentsubstrate, writing a pattern using electron beam, and developing to forma resist pattern. Using the resulting resist pattern as an etch mask,the light-shielding film is etched into a light-shielding pattern. In anattempt to miniaturize the light-shielding pattern, if processing iscarried out while maintaining the thickness of the resist film at thesame level as in the prior art prior to the miniaturization, the ratioof film thickness to pattern, known as aspect ratio, becomes higher. Asa result, the resist pattern profile is degraded, preventing effectivepattern transfer, and in some cases, there occurs resist patterncollapse or stripping. Therefore, the miniaturization must entail athickness reduction of resist film.

As to the light-shielding film material which is etched using the resistas an etch mask, on the other hand, a number of materials have beenproposed. In practice, chromium compound films are always employedbecause there are known a number of findings with respect to theiretching and the standard process has been established. Typical of suchfilms are light-shielding films composed of chromium compounds necessaryfor photomask blanks for ArF excimer laser lithography, which includechromium compound films with a thickness of 50 to 77 nm as reported inJP-A 2003-195479, JP-A 2003-195483, and Japanese Patent No. 3093632.

However, oxygen-containing chlorine dry etching which is a common dryetching process for chromium based films such as chromium compound filmsoften has a capability of etching organic films to some extent. Ifetching is carried out through a thin resist film, accurate transfer ofthe resist pattern is difficult. It is a task of some difficulty for theresist to have both a high resolution and etch resistance that allowsfor high accuracy etching. Then, for the purpose of achieving highresolution and high accuracy, the light-shielding film material has tobe reviewed so as to find a transition from the approach relying only onthe resist performance to the approach of improving the light-shieldingfilm performance as well.

Also, as to light-shielding film materials other than the chromium basedmaterials, a number of studies have been made. One example of the lateststudies is the use of tantalum in the light-shielding film for ArFexcimer laser lithography. See JP-A 2001-312043.

On the other hand, it has long been a common practice to use a hard maskfor reducing the load on resist during dry etching. For example, JP-A63-85553 discloses MoSi₂ overlaid with a SiO₂ film, which is used as anetch mask during dry etching of MoSi₂ with chlorine gas. It is describedthat the SiO₂ film can also function as an antireflective film.

From the past, studies have been made on metal silicide films which canbe more readily etched under fluorine dry etching conditions that causeleast damages to the resist film, especially molybdenum silicide films.They are disclosed, for example, in JP-A 63-85553, JP-A 1-142637, andJP-A 3-116147, all of which basically use a film of silicon andmolybdenum=2:1. Also, JP-A 4-246649 discloses a metal silicide film,which has not been applied to the actual fabrication because of somepractical problems. The actual fabrication process accommodates theminiaturization demand by improving conventional chromium-basedlight-shielding films.

For masks utilizing the ultra-resolution technology such as halftonephase shift masks and Levenson phase shift masks, on the other hand, themask processing process includes the step of removing a portion of thelight-shielding film which causes a phase shift to light, during whichstep selective etching must be possible between the light-shielding filmand the underlying film or substrate. Since conventional chromium-basedmaterials are superior in this sense, few studies have been made on theuse of other materials.

DISCLOSURE OF THE INVENTION

The inventors continued efforts to develop a material and method forforming a finer mask pattern at a higher accuracy. Most of ourexperiments used chromium-based materials commonly employed in the priorart, and selected dry etching conditions containing chlorine and oxygenin transferring a resist pattern to a chromium-based material film. Inthis method, a photoresist is first coated onto a photomask blank havinga light-shielding film of chromium-based material. The resist film issubjected to electron beam exposure and subsequent development, forexample, for thereby forming a resist pattern. Using the resist film asan etching mask, the chromium-based material film is etched fortransferring the resist pattern to the chromium-based material film.

In this method, however, when the pattern width becomes finer, forexample, when a resist pattern of straight lines of up to 0.4 μm wide asa pattern model is transferred to a chromium light-shielding film, asignificant pattern density dependency is observed. In some cases, theresulting pattern has noticeable errors relative to the resist patternformed on the photomask blank. That is, an isolated line with less filmpattern left therearound and an isolated space with more film patternleft therearound have a significant difference in resist patterntransfer characteristics so that it is very difficult to make a highaccuracy mask.

This problem is not serious when resist pattern features of more than0.4 μm are used. In the manufacture of a photomask, the problem is notso serious if the photomask is intended for the exposure of a resistpattern of the order of 0.3 μm, but becomes serious if the photomask isto form resist pattern features of 0.1 μm or less.

The above problem might be overcome by avoiding the use ofchromium-based material in the light-shielding film. In the prior art,particularly when a light-shielding film of chromium-based material isused in processing a phase shift pattern, the phase shift pattern isprecisely transferred to the phase shift film or substrate using thepatterned light-shielding film of chromium-based material as a hardmask. After this processing, the unnecessary light-shielding film can beetched away without causing damages to the phase shift film orsubstrate. In constructing a photomask blank from a new light-shieldingfilm, a new issue arises how to acquire the hard mask function.

An object of the invention is to provide a photomask blank which endowsa photomask with both a high resolution and a high accuracy etchingcapability for forming a finer photomask pattern, especially as neededin the photolithography involving exposure to light of a wavelengthequal to or less than 250 nm such as ArF excimer laser light, i.e., aphotomask blank having a sufficient process accuracy of etch processingto form a pattern with minimized pattern density dependency, or even aphotomask blank having a minimized possibility of causing damages to aphase shift film and a transparent substrate below the light-shieldingfilm during removal of the light-shielding film and a processingaccuracy substantially equivalent to that attainable with the prior artlight-shielding films of chromium-based material; and a photomaskobtained by patterning the photomask blank.

Regarding the accuracy of etch processing to a pattern with a size equalto or less than 0.4 μm, the inventors have found the following. Even afilm of chromium-based material can be reduced in pattern densitydependency if it is made fully thin, but a chromium-based material filmwithin such thickness range is short in light shielding. As comparedwith the dry etching of chromium-based materials under chlorine andoxygen-containing conditions, a film which can be processed by fluorinedry etching exhibits reduced pattern density dependency during fluorinedry etching, so that the film can be precision processed even at asufficient thickness to serve as a light-shielding film. A filmcontaining a transition metal and silicon is appropriate to this end.

Even a film of chromium-based material has reduced pattern densitydependency if it is fully thin. Then the chromium-based material filmcan be utilized in precision processing of patterns if the film has aminimum thickness so that it has no impact on optical properties (e.g.,transmittance) of a pattern formed on a photomask.

On the basis of these findings, the inventors have found the following.A light-shielding film consists of a single layer composed of a materialcontaining a transition metal and silicon or multiple layers includingat least one layer composed of a material containing a transition metaland silicon; an etch stop film is disposed on a transparent substrate,optionally with another film intervening therebetween, and particularlywhen a phase shift film is to be used, the phase shift film interveningtherebetween, the etch stop film of single layer or multilayerconstruction being resistant to fluorine dry etching and removable bychlorine dry etching, preferably the etch stop film being composed ofchromium alone or a chromium compound containing a transition metal andat least one element of oxygen, nitrogen and carbon; the light-shieldingfilm is disposed contiguous to the etch stop film; and an antireflectivefilm consisting of a single layer or multiple layers is disposed on thelight-shielding film. The lamination of films as above results in aphotomask blank having the advantages that the light-shielding film canbe processed at a high accuracy independent of the pattern density, thelight-shielding film can be removed without causing damages to thetransparent substrate and phase shift film, and even when the phaseshift film and transparent substrate are processed by etching afterformation of a pattern of the light-shielding film, a pattern can betransferred to the phase shift film and transparent substrate at a highaccuracy.

Accordingly, the present invention provides a photomask blank and aphotomask as defined below.

-   [1] A photomask blank from which is produced a photomask comprising    a transparent substrate and a mask pattern formed thereon including    transparent regions and effectively opaque regions to exposure    light, said photomask blank comprising

a transparent substrate,

an etch stop film disposed on the substrate, optionally with anotherfilm intervening therebetween, said etch stop film of single layer ormultilayer construction being resistant to fluorine dry etching andremovable by chlorine dry etching,

a light-shielding film disposed contiguous to said etch stop film andconsisting of a single layer composed of a material containing atransition metal and silicon or multiple layers including at least onelayer composed of a material containing a transition metal and silicon,and

an antireflective film disposed contiguous to said light-shielding filmand consisting of a single layer or multiple layers.

-   [2] The photomask blank of [1], wherein said etch stop film is    composed of chromium alone or a chromium compound containing    chromium and at least one element selected from oxygen, nitrogen and    carbon.-   [3] The photomask blank of [1], wherein said etch stop film is    composed of tantalum alone or a tantalum compound containing    tantalum and free of silicon.-   [4] The photomask blank of any one of [1] to [3], wherein said etch    stop film has a thickness of 2 to 20 nm.-   [5] The photomask blank of any one of [1] to [4], wherein the    material of which the layer of said light-shielding film is composed    contains a transition metal and silicon in a ratio of 1:4-15.-   [6] The photomask blank of any one of [1] to [5], wherein the    material of which the layer of said light-shielding film is composed    is an alloy of a transition metal with silicon or a transition metal    silicon compound containing a transition metal, silicon and at least    one element selected from oxygen, nitrogen and carbon.-   [7] The photomask blank of any one of [1] to [5], wherein the    material of which the layer of said light-shielding film is composed    is a transition metal silicon compound containing a transition    metal, silicon and nitrogen.-   [8] The photomask blank of [7], wherein said light-shielding film    has a nitrogen content of 5 atom % to 40 atom %.-   [9] The photomask blank of any one of [1] to [8], wherein said    light-shielding film consists of multiple layers including a layer    composed of a chromium compound containing chromium and at least one    element selected from oxygen, nitrogen and carbon.-   [10] The photomask blank of any one of [1] to [9], wherein said    light-shielding film consists of two layers, a first light-shielding    layer formed adjacent to the transparent substrate and a second    light-shielding layer formed adjacent to the antireflective film,    the first light-shielding layer is composed of a transition metal    silicon compound containing a transition metal, silicon and oxygen    and/or nitrogen, and the second light-shielding layer is composed of    a chromium compound containing chromium and oxygen and/or nitrogen.-   [11] The photomask blank of any one of [1] to [10], wherein said    light-shielding film consists of multiple layers, among which a    layer disposed contiguous to said antireflective film has an    extinction coefficient k of at least 1.5 relative to exposure light.-   [12] The photomask blank of any one of [1] to [11], wherein said    light-shielding film has a thickness of 10 to 80 nm.-   [13] The photomask blank of any one of [1] to [12], wherein said    antireflective film includes a layer of a transition metal silicon    compound containing a transition metal, silicon, and oxygen and/or    nitrogen.-   [14] The photomask blank of any one of [1] to [13], wherein said    antireflective film includes a layer of chromium alone or a chromium    compound containing chromium and oxygen and/or nitrogen.-   [15] The photomask blank of any one of [1] to [14], wherein said    antireflective film consists of two layers, a first antireflective    layer formed adjacent to the transparent substrate and a second    antireflective layer formed remote from the transparent substrate,    the first antireflective layer is composed of a transition metal    silicon compound comprising a transition metal, silicon and oxygen    and/or nitrogen, and the second antireflective layer is composed of    a chromium compound containing chromium and oxygen and/or nitrogen.-   [16] The photomask blank of [14] or [15], wherein in said    antireflective film, the layer of chromium compound has a chromium    content of at least 50 atom %.-   [17] The photomask blank of any one of [1] to [16], further    comprising an etching mask film disposed contiguous to said    antireflective film and consisting of a single layer or multiple    layers which are resistant to fluorine dry etching and removable by    chlorine dry etching.-   [18] The photomask blank of [17], wherein said etching mask film is    composed of chromium alone or a chromium compound containing    chromium and at least one element selected from oxygen, nitrogen and    carbon.-   [19] The photomask blank of [17] or [18], wherein said etching mask    film has a thickness of 2 to 30 nm.-   [20] The photomask blank of any one of [1] to [19], wherein said    transition metal is at least one element selected from the group    consisting of titanium, vanadium, cobalt, nickel, zirconium,    niobium, molybdenum, hafnium, tantalum, and tungsten.-   [21] The photomask blank of any one of [1] to [19], wherein said    transition metal is molybdenum.-   [22] The photomask blank of any one of [1] to [21], wherein a phase    shift film intervenes as the other film.-   [23] The photomask blank of [22], wherein said phase shift film is a    halftone phase shift film.-   [24] A photomask obtained by patterning the photomask blank of any    one of [1] to [23].

BENEFITS OF THE INVENTION

As compared with photomask blanks having conventional light-shieldingfilms of chromium-based materials, the photomask blank of the inventionhas the advantage that when the light-shielding film is dry etched toform a pattern, the variation of pattern feature size arising from thepattern density dependency is reduced. This enables to produce a mask ata high accuracy. When the photomask blank of the invention is applied toa halftone phase shift mask, chromeless mask or Levenson mask, thelight-shielding film can be selectively removed by dry etching withoutcausing damages to any film underlying the light-shielding film andtransparent substrate, enabling phase control at a high accuracy. Thenphotomasks for super-resolution exposure can be manufactured at a highaccuracy.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross-sectional view showing one exemplary photomask blankin a first embodiment of the invention, FIG. 1A corresponding to alight-shielding film disposed directly on a transparent substrate andFIG. 1B corresponding to a light-shielding film disposed on atransparent substrate via a phase shift film.

FIG. 2 is a cross-sectional view showing one exemplary photomask blankin a second embodiment of the invention, FIG. 2A corresponding to alight-shielding film disposed directly on a transparent substrate andFIG. 2B corresponding to a light-shielding film disposed on atransparent substrate via a phase shift film.

FIG. 3 is a cross-sectional view showing one exemplary photomask blankin a third embodiment of the invention, FIG. 3A corresponding to alight-shielding film disposed directly on a transparent substrate andFIG. 3B corresponding to a light-shielding film disposed on atransparent substrate via a phase shift film.

FIG. 4 is a cross-sectional view showing one exemplary photomask blankin a fourth embodiment of the invention, FIG. 4A corresponding to alight-shielding film disposed directly on a transparent substrate andFIG. 4B corresponding to a light-shielding film disposed on atransparent substrate via a phase shift film.

FIG. 5 is a cross-sectional view showing one exemplary photomask blankin a fifth embodiment of the invention, FIG. 5A corresponding to alight-shielding film disposed directly on a transparent substrate andFIG. 5B corresponding to a light-shielding film disposed on atransparent substrate via a phase shift film.

FIG. 6 schematically illustrates steps of a method for producing aphotomask according to the invention, the method using the photomaskblank of the first embodiment and producing a Levenson mask (photomaskproducing procedure A).

FIG. 7 schematically illustrates steps of a method for producing aphotomask according to the invention, the method using the photomaskblank of the first embodiment and producing a tritone phase shift mask(photomask producing procedure B).

FIG. 8 schematically illustrates steps of a method for producing aphotomask according to the invention, the method using the photomaskblank of the second embodiment and producing a Levenson mask (photomaskproducing procedure C).

FIG. 9 schematically illustrates steps of a method for producing aphotomask according to the invention, the method using the photomaskblank of the second embodiment and producing a zebra-type chromelessmask (photomask producing procedure D), FIGS. 9A, 9C, 9E, 9G and 9Ibeing cross-sectional views and FIGS. 9B, 9D, 9F, 9H and 9J being planviews.

FIG. 10 schematically illustrates steps of a method for producing aphotomask according to the invention, i.e., subsequent steps from FIG. 9of the method using the photomask blank of the second embodiment andproducing a zebra-type chromeless mask (photomask producing procedureD), FIGS. 10A, 10C, 10E, 10G and 10I being cross-sectional views andFIGS. 10B, 10D, 10F, 10H and 10J being plan views.

FIG. 11 schematically illustrates steps of a method for producing aphotomask according to the invention, the method using the photomaskblank of the second embodiment and producing a tritone phase shift mask(photomask producing procedure E).

FIG. 12 schematically illustrates steps of a method for producing aphotomask according to the invention, the method using the photomaskblank of the third embodiment and producing a Levenson mask (photomaskproducing procedure F).

FIG. 13 schematically illustrates steps of a method for producing aphotomask according to the invention, the method using the photomaskblank of the third embodiment and producing a tritone phase shift mask(photomask producing procedure G).

FIG. 14 schematically illustrates steps of a method for producing aphotomask according to the invention, the method using the photomaskblank of the fourth embodiment and producing a halftone phase shift mask(photomask producing procedure H).

FIG. 15 schematically illustrates steps of a method for producing aphotomask according to the invention, the method using the photomaskblank of the fifth embodiment and producing a halftone phase shift mask(photomask producing procedure I).

FIG. 16 is a photomicrograph in cross section of an intermediate samplehaving an antireflective film, light-shielding film and etch stop filmpatterned during the production of a Levenson mask in Example 2, showingits light-shielding pattern, and a schematic cross-sectional view of theintermediate sample.

FIG. 17 is a graph showing the results of a CD linearity test ofphotomask blanks of Example 4 and Comparative Example.

FIG. 18 is a schematic cross-sectional view of a photomask blank inComparative Example.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

As used in connection with dry etching, the term “susceptible” meansthat the material can be etched by dry etching, and the term “resistant”means that the material withstands dry etching. As used herein, the term“fluorine dry etching” refers to dry etching using an etchant gascontaining fluorine, and the term “chlorine dry etching” refers to dryetching using an etchant gas containing chlorine and optionally oxygen.

The present invention is directed to a photomask blank from which aphotomask comprising a transparent substrate and a mask pattern formedthereon including transparent regions and effectively opaque regions toexposure light is produced. The photomask blank comprises a transparentsubstrate, an etch stop film disposed on the substrate, optionally withanother film intervening therebetween, the etch stop film of singlelayer or multilayer construction being resistant to fluorine dry etchingand removable by chlorine dry etching, a light-shielding film disposedcontiguous to the etch stop film and consisting of a single layercomposed of a material containing a transition metal and silicon ormultiple layers including at least one layer composed of a materialcontaining a transition metal and silicon, and an antireflective filmdisposed contiguous to the light-shielding film and consisting of asingle layer or multiple layers.

The etch stop film is a film serving for a function of preventing theother film underlying the light-shielding film, typically phase shiftfilm, and the transparent substrate from being etched during fluorinedry etching of the light-shielding film; the light-shielding film is afilm serving predominantly for a shielding function to exposure light;and the antireflective film (ARF) is a film serving predominantly for anantireflection function to exposure light or inspection light, that is,a function of reducing reflectance, on use in photomask form.

A light-shielding film containing a transition metal and silicon is usedbecause of the inventors' discovery described below.

Aiming at photomasks for use in semiconductor lithography with a patternrule equal to or less than 0.1 μm, the inventors have investigated aphotomask blank capable of being processed to a fine size and at a highaccuracy and a method of producing a photomask therefrom. As the patternsize of a light-shielding film formed on a photomask becomes smaller,the absolute value of errors involved in mask processing must besmaller. In some cases, however, errors become rather large due to theinfluence of pattern size.

A chromium-based light-shielding film used in the prior art is processedby a standard technique of oxygen-containing chlorine dry etching whileusing a resist pattern as an etching mask. Problems arising during theprocessing are not so serious when the pattern size exceeds 0.4 μm. Onthe other hand, masks for use in ArF excimer laser exposure must have avery high accuracy if the light-shielding film has a pattern size equalto or less than 0.4 μm (which corresponds to a pattern design rule of0.1 μm because of one-fourth reduction projection).

An attempt to transfer a pattern with a size equal to or less than 0.4μm to a chromium-based light-shielding film has revealed the enhancementof pattern density dependency in that in processing a photomask blankinto a photomask, the transfer characteristics associated with theresist pattern largely differ between an area where patterns areisolated (isolated pattern area) and an area where spaces (the film isabsent) are isolated (isolated space area). It is expected that thisproblem is exaggerated when the size of a pattern to be transferred isfurther reduced to 0.2 μm or less, imposing substantial impact on theformation of OPC patterns or the like.

Specifically, as a typical photomask blank model for an ArF lithographymask, there was furnished a photomask blank comprising a CrNlight-shielding film of 26 nm thick (Cr:N=9:1 in atomic ratio) and aCrON antireflective film of 20 nm thick (Cr:O:N=4:5:1 in atomic ratio)deposited in sequence on a transparent substrate. On this photomaskblank, a 1:9 line-and-space pattern (isolated pattern model) and a 9:1line-and-space pattern (isolated space model) were formed as anisolated/grouped line pattern model having a line width varying from 1.6μm to 0.2 μm at intervals of 0.1 μm, by chlorine and oxygen dry etchingunder etching conditions: a Cl₂ flow rate of 20 sccm, an O₂ flow rate of9 sccm, a He flow rate of 80 sccm, and a chamber internal pressure of 2Pa. As a result, in the isolated space, the size error over the rangefrom 1.6 μm to 0.2 μm amounted to 5.3 nm in terms of the differencebetween minimum and maximum widths. In the isolated pattern, the widthwas 3.8 nm in the range from 1.6 μm to 0.5 μm, but 13.8 nm in the rangefrom 1.6 μm to 0.2 μm. A phenomenon was observed that the etching ratesubstantially differs (finished thick) among fine isolated patternsequal to or less than 0.4 μm.

Under the expectation that the line density dependency is closelycorrelated to etching conditions, a test was carried out on a transitionmetal silicide light-shielding film as the light-shielding film whichcan be processed under different etching conditions. As a photomaskblank model for an ArF lithography mask, there was furnished a photomaskblank comprising a MoSiN light-shielding film of 23 nm thick(Mo:Si:N=1:3:1.5 in atomic ratio) and a MoSiN antireflective film of 18nm thick (compositionally graded in a thickness direction fromMo:Si:N=1:3:1.5 in atomic ratio on the light-shielding film side toMo:Si:N=1:5:5 in atomic ratio on the side remote from the transparentsubstrate) deposited in sequence on a transparent substrate. On thisphotomask blank, a 1:9 line-and-space pattern (isolated pattern model)and a 9:1 line-and-space pattern (isolated space model) were formed asan isolated/grouped line pattern model having a line width varying from1.6 μm to 0.2 μm at intervals of 0.1 μm, by fluorine dry etching underconditions: C₂F₆ at 20 sccm and chamber internal pressure 2 Pa. As aresult, in the isolated space, the size error over the range from 1.6 μmto 0.2 μm amounted to 2.3 nm in terms of the difference between minimumand maximum widths. In the isolated pattern, the width was 9.0 nm in therange from 1.6 μm to 0.2 μm, indicating that the problem of line densitydependency is significantly ameliorated.

While all currently used super-resolution photomasks including halftonephase shift masks, chromeless masks and Levenson masks are designed toincrease the light contrast in lithography by utilizing the interferenceeffect of phase different light, the phase of light transmitted by themask is controlled by the material and film thickness of a phase shifterformed on the mask. In the manufacture of super-resolution photomasksutilizing the phase shift effect as currently widely employed, a patternof phase shifter is formed by a method involving providing a photomaskblank having a light-shielding film deposited thereon, first patterningthe light-shielding film formed on the phase shift film, thentransferring the pattern to the phase shift film. Therefore, it is veryimportant that the pattern of the light-shielding film be accuratelydefined.

The importance is not limited to this point. Before a phase shifter iscompleted, the light-shielding film on the phase shift film and thetransparent substrate must be removed to allow for incidence of light tothe phase shifter. If the phase shift film and transparent substrate aredamaged during removal of the light-shielding film, then errors areintroduced into the phase difference created by the phase shifter. It isthus important that the light-shielding film be removed without causingdamages to any film underlying the light-shielding film such as thephase shift film and the transparent substrate.

The ordinary phase shifter used in the phase shift mask is a filmcomposed of transition metal silicide having oxygen and/or nitrogenadded thereto in the case of halftone phase shift masks, or thetransparent substrate itself or a layer structure of silicon oxide orthe like in the case of chromeless masks and Levenson masks. In eithercase, they are materials which are processed by fluorine dry etching.Then, the light-shielding film materials used in the prior art arechromium-based materials. The chromium-based materials have beenadvantageous for the light-shielding film because they are resistant tofluorine dry etching conditions, perform well as an etching mask duringfluorine dry etching, and can be removed under chlorine-containing dryetching conditions that do not attack the silicon-containing materials,for example, chlorine dry etching as typified by dry etching using anetchant gas containing chlorine and oxygen.

On the other hand, the problem that the accuracy of processing ofconventional chromium-based light-shielding film materials lowers due tothe pattern density dependency becomes quite serious in the manufactureof a photomask intended for exposure of a pattern with a feature sizeequal to or less than 0.1 μm. The photomask blank of the inventionsolves the problem of processing accuracy by using a material containinga transition metal and silicon, which is susceptible to fluorine dryetching, in at least a portion, preferably the entirety of alight-shielding film, and establishes an etching selectivity relative toany film underlying the light-shielding film such as the phase shiftfilm and the substrate, using an etch stop film of a single layer ormultilayer structure.

Accordingly, the etch stop film used herein must be a film which isresistant to fluorine dry etching and removable by dry etching underchlorine-containing conditions that are etching conditions causing nodamages to the phase shift film and transparent substrate. The preferredmaterials having such functions include chromium-based materials andmaterials containing tantalum, free of silicon.

The preferred chromium-based materials include chromium alone andchromium compounds containing chromium and at least one element selectedfrom oxygen, nitrogen and carbon and more preferably free of silicon.More illustrative examples of the chromium compound include chromiumoxide, chromium nitride, chromium oxynitride, chromium oxycarbide,chromium nitride carbide, and chromium oxide nitride carbide.

The chromium-based materials are highly resistant to fluorine dryetching and at the same time, etchable under dry etching conditionscontaining chlorine and oxygen. Since the chromium-based materials canbe removed by dry etching under such conditions without causing damageto the material containing a transition metal, silicon, and oxygenand/or nitrogen used in a phase shift film, typically a halftone phaseshift film, or the silicon oxide material disposed beneath thelight-shielding film in the case of a chromeless mask or Levenson mask,they function well as an etch stop film for solving the outstandingproblems.

On the other hand, the tantalum-containing material loses resistance tofluorine dry etching if it contains silicon. However, in the absence ofsilicon, a tantalum-containing material, for example, tantalum alone hasa sufficient resistance to fluorine dry etching to allow for selectiveetching relative to the silicon-containing material. Also, tantalumcompounds containing tantalum, free of silicon, such as materials basedon tantalum and zirconium, or tantalum and hafnium offer a satisfactoryetching selectivity ratio relative to the silicon-containing material.It is noted that unlike the chromium-based materials, thetantalum-containing materials can be etched by oxygen-free chlorine dryetching.

Depending on the design of a mask to be produced, the etch stop filmused herein is deposited on a transparent substrate directly or via ahalftone phase shift film, a transparent phase shift film or the like(while another etch stop film may intervene between the transparentsubstrate and the phase shift film).

The etch stop film should preferably have a thickness of at least 2 nm,more preferably at least 5 nm. Then the etch stop film exerts itsfunction so that any film underlying the etch stop film or substrate maynot be damaged when a light-shielding film containing a transition metaland silicon is etched. The upper limit of the etch stop film thicknessis generally up to 20 nm, preferably up to 15 nm.

As will be described later, in some cases, depending on the type of aphotomask to be produced, the etch stop film is used as an etching maskin order to etch the underlying film or substrate at a high accuracy ina position selective fashion. In such cases, the etch stop film may bethicker if necessary, for example, a thickness of 2 to 55 nm. Theinventors have found that if the etch stop film is too thick, there is apossibility that when the film is etched under chlorine andoxygen-containing conditions, substantial side etching occurs, ratherresulting in a lowering of size accuracy during subsequent processing ofthe underlying film. To avoid the problem of side etching, the etch stopfilm should preferably have a thickness of not more than 55 nm, morepreferably not more than 40 nm, and even more preferably not more than30 nm. The same problem arises when a chromium-based material is used aspart of the etching mask film or light-shielding film to be describedlater, and the above-described thickness range is preferred for higheraccuracy size control.

For the etch stop film of chromium-based material, when the etch stopfilm functions as an etching mask as described above, it shouldpreferably be constructed from multiple layers, for example, two orthree layers, at least one of which is composed of chromium alone or achromium compound containing chromium and at least one of oxygen,nitrogen and carbon, with a chromium content of at least 50 atom %. Thenthe etch stop film can exert an etching mask function without a need toincrease its thickness.

The etch stop film can be deposited by well-known methods. Among others,the sputtering process is preferable. The sputtering process may beeither DC sputtering, RF sputtering or the like.

Deposition of the etch stop film may be performed by a method as used inthe prior art for chromium-based light-shielding films andantireflective films. One commonly used method is by sputtering achromium or tantalum target in an inert gas such as argon, a reactivegas such as oxygen-containing gas, nitrogen-containing gas orcarbon-containing gas, or a mixture of an inert gas and a reactive gas.See JP-A 7-140635, for example.

When the etch stop film used herein is composed of a chromium-basedmaterial and has less adhesion to any component disposed contiguousthereto such as a light-shielding film, phase shift film or substrate sothat pattern defects may frequently occur, the etch stop film, if it isa single layer, is preferably constructed as a single layer whosecomposition is continuously graded in a thickness direction so that oneor both of the side surface contiguous to the transparent substrate orthe other film disposed between the transparent substrate and thelight-shielding film and the side surface contiguous to thelight-shielding film are composed of a chromium compound containingoxygen and/or nitrogen.

If the etch stop film is a multilayer film, on the other hand, the etchstop film is preferably constructed from multiple layers whosecomposition is graded stepwise in a thickness direction so that one orboth of the layer contiguous to the transparent substrate or the otherfilm disposed between the transparent substrate and the light-shieldingfilm and the layer contiguous to the light-shielding film are composedof a chromium compound containing oxygen and/or nitrogen. Theconstruction of the etch stop film in this way improves the adhesion.The etch stop film of the above construction can be readily formed bycontrolling the parameters of reactive sputtering.

Described below are the light-shielding film and antireflective filmdeposited on the etch stop film.

In the photomask blank of the invention, the light-shielding film isconstructed by a single layer composed of a material containing atransition metal and silicon or multiple layers including at least onelayer composed of a material containing a transition metal and silicon.On the other hand, the antireflective film is constructed by a singlelayer or multiple layers. The light-shielding film and theantireflective film are preferably constructed such that thelight-shielding film and antireflective film can be processed by asingle dry etching step or two dry etching steps in order to avoidcomplication of etch processing steps beyond the necessity.

The construction allowing the light-shielding film and antireflectivefilm to be processed by a single dry etching step includes theconstruction wherein the light-shielding film and antireflective filmare entirely composed of materials containing a transition metal andsilicon which are susceptible to fluorine dry etching (the firstembodiment). Specifically, one exemplary blank is illustrated in FIG. 1Aas comprising an etch stop film 9, a light-shielding film 2 and anantireflective film 3 disposed on a transparent substrate 1 in thedescribed sequence. The blank having a light-shielding film disposed ona transparent substrate via another intervening film includes a blankhaving a phase shift film intervening as the other film betweenlaminated films. Specifically, one exemplary blank is illustrated inFIG. 1B as comprising a phase shift film 8, an etch stop film 9, alight-shielding film 2 and an antireflective film 3 disposed on atransparent substrate 1 in the described sequence.

The blank may also be constructed so as to include on the antireflectivefilm an etching mask film composed of a material which is resistant tofluorine dry etching (the second embodiment). Specifically, oneexemplary blank is illustrated in FIG. 2A as comprising an etch stopfilm 9, a light-shielding film 2, an antireflective film 3 and anetching mask film 4 disposed on a transparent substrate 1 in thedescribed sequence. The blank having a light-shielding film disposed ona transparent substrate via another intervening film includes a blankhaving a phase shift film intervening as the other film betweenlaminated films. Specifically, one exemplary blank is illustrated inFIG. 2B as comprising a phase shift film 8, an etch stop film 9, alight-shielding film 2, an antireflective film 3 and etching mask film 4disposed on a transparent substrate 1 in the described sequence.

The effect of ameliorating the problem of pattern density dependencyarising in forming a pattern with a feature size equal to or less than0.4 μm becomes most outstanding with these first and second embodiments.

The construction allowing the light-shielding film and antireflectivefilm to be processed by two dry etching steps includes the constructionwherein the light-shielding film is composed of a material containing atransition metal and silicon which is susceptible to fluorine dryetching and the antireflective film includes a layer, disposed adjacentto the light-shielding film, composed of a material susceptible tofluorine dry etching and a layer, disposed remote from thelight-shielding film, composed of a material resistant to fluorine dryetching (the third embodiment). Specifically, one exemplary blank isillustrated in FIG. 3A as comprising an etch stop film 9, alight-shielding film 2 susceptible to fluorine dry etching, and anantireflective film 30 consisting of two layers: an antireflective layer31 susceptible to fluorine dry etching (first antireflective layer) andan antireflective layer 51 resistant to fluorine dry etching (secondantireflective layer), disposed on a transparent substrate 1 in thedescribed sequence. The blank having a light-shielding film disposed ona transparent substrate via another intervening film includes a blankhaving a phase shift film intervening as the other film betweenlaminated films. Specifically, one exemplary blank is illustrated inFIG. 3B as comprising a phase shift film 8, an etch stop film 9, alight-shielding film 2 susceptible to fluorine dry etching, and anantireflective film 30 consisting of two layers: an antireflective layer31 susceptible to fluorine dry etching (first antireflective layer) andan antireflective layer 51 resistant to fluorine dry etching (secondantireflective layer), disposed on a transparent substrate 1 in thedescribed sequence.

Also included is the construction wherein the light-shielding film iscomposed of a material containing a transition metal and silicon whichis susceptible to fluorine dry etching and the antireflective film iscomposed of a material which is resistant to fluorine dry etching (thefourth embodiment). Specifically, one exemplary blank is illustrated inFIG. 4A as comprising an etch stop film 9, a light-shielding film 2susceptible to fluorine dry etching, and an antireflective film 5resistant to fluorine dry etching, disposed on a transparent substrate 1in the described sequence. The blank having a light-shielding filmdisposed on a transparent substrate via another intervening filmincludes a blank having a phase shift film intervening as the other filmbetween laminated films. Specifically, one exemplary blank isillustrated in FIG. 4B as comprising a phase shift film 8, an etch stopfilm 9, a light-shielding film 2 susceptible to fluorine dry etching,and an antireflective film 5 resistant to fluorine dry etching, disposedon a transparent substrate 1 in the described sequence.

Also included is the construction wherein the light-shielding filmincludes a layer, disposed adjacent to the transparent substrate,composed of a material containing a transition metal and silicon whichis susceptible to fluorine dry etching and a layer, disposed adjacent tothe antireflective film, composed of a material which is resistant tofluorine dry etching and the antireflective film is composed of amaterial which is resistant to fluorine dry etching (the fifthembodiment). Specifically, one exemplary blank is illustrated in FIG. 5Aas comprising an etch stop film 9, a light-shielding film 20 consistingof two layers: a light-shielding layer 21 susceptible to fluorine dryetching (first light-shielding layer) and a light-shielding layer 22resistant to fluorine dry etching (second light-shielding layer), and anantireflective film 5 resistant to fluorine dry etching, disposed on atransparent substrate 1 in the described sequence. The blank having alight-shielding film disposed on a transparent substrate via anotherintervening film includes a blank having a phase shift film interveningas the other film between laminated films. Specifically, one exemplaryblank is illustrated in FIG. 5B as comprising a phase shift film 8, anetch stop film 9, a light-shielding film 20 consisting of two layers: alight-shielding layer 21 susceptible to fluorine dry etching (firstlight-shielding layer) and a light-shielding layer 22 resistant tofluorine dry etching (second light-shielding layer), and anantireflective film 5 resistant to fluorine dry etching, disposed on atransparent substrate 1 in the described sequence.

It is noted that a film or layer resistant to fluorine dry etchingshould have a reduced thickness sufficient to avoid the problem oftransferred pattern's density dependency during dry etching. Then theetching mask film avoids the problem of pattern density dependency. Ascompared with prior art photomask blanks using fluorine dry etchingresistant materials such as chromium-based materials in the entirety ofthe light-shielding film and antireflective film, the blank of theinvention is successful in apparently minimizing the transferredpattern's density dependency.

More particularly, a film or layer which is resistant to fluorine dryetching of the light-shielding film and antireflective film may functionas an etching mask when the light-shielding film containing a transitionmetal and silicon, a layer of a material containing a transition metaland silicon to constitute the light-shielding film and a layer of amaterial containing a transition metal and silicon to constitute theantireflective film are etched, and also function as an etching maskwhen an underlying film such as a phase shift film and the transparentsubstrate are etched.

The transition metal and silicon-containing materials susceptible tofluorine dry etching used herein to form the light-shielding film andantireflective film include alloys of a transition metal with silicon,and transition metal silicon compounds containing a transition metal,silicon, and at least one element selected from oxygen, nitrogen andcarbon, preferably transition metal silicon compounds containing atransition metal, silicon, and oxygen and/or nitrogen. More illustrativeexamples of the transition metal silicon compound include transitionmetal silicon oxide, transition metal silicon nitride, transition metalsilicon oxynitride, transition metal silicon oxycarbide, transitionmetal silicon nitride carbide, and transition metal silicon oxidenitride carbide, with the transition metal silicon nitride being mostpreferred.

The transition metal is preferably at least one element selected fromthe group consisting of titanium, vanadium, cobalt, nickel, zirconium,niobium, molybdenum, hafnium, tantalum, and tungsten. Inter alia,molybdenum is more preferred for dry etching amenability.

The light-shielding film and the antireflective film each may consist ofa single layer or multiple layers or even a single layer with continuouscompositional grading in a thickness direction or multiple layers withstepwise compositional grading in a thickness direction.

With respect to the composition of the material containing a transitionmetal and silicon, the light-shielding film preferably has a compositionconsisting essentially of 10 atom % to 95 atom %, specifically 30 atom %to 95 atom % of silicon, 0 atom % to 50 atom %, specifically 0 atom % to30 atom % of oxygen, 0 atom % to 40 atom %, specifically 1 atom % to 20atom % of nitrogen, 0 atom % to 20 atom %, specifically 0 atom % to 5atom % of carbon, and 0 atom % to 35 atom %, specifically 1 atom % to 20atom % of transition metal.

The light-shielding film, when its composition is graded in a thicknessdirection, preferably has a composition consisting essentially of 10atom % to 95 atom %, specifically 15 atom % to 95 atom % of silicon, 0atom % to 60 atom %, specifically 0 atom % to 30 atom % of oxygen, 0atom % to 57 atom %, specifically 1 atom % to 40 atom % of nitrogen, 0atom % to 30 atom %, specifically 0 atom % to 20 atom % of carbon, and 0atom % to 35 atom %, specifically 1 atom % to 20 atom % of transitionmetal. Better etching characteristics are obtained particularly when thenitrogen content is 1 atom % to 40 atom %.

During etching under chlorine and oxygen-containing etching conditions,for example, etching of the etch stop film, even transition metal andsilicon-containing materials can be etched to some extent. If thetransition metal and silicon-containing material is a transition metalsilicon compound containing a transition metal, silicon and nitrogen,more preferably with a nitrogen content of 1 atom % to 40 atom %, evenmore preferably 5 atom % to 40 atom %, the light-shielding film andantireflective film of transition metal and silicon-containing materialsare prevented from being damaged even when etching conditions withdamaging potential are employed. These films allow for a high degree offreedom to processing conditions.

On the other hand, the antireflective film preferably has a compositionconsisting essentially of 10 atom % to 80 atom %, specifically 30 atom %to 50 atom % of silicon, 0 atom % to 60 atom %, specifically 0 atom % to40 atom % of oxygen, 0 atom % to 57 atom %, specifically 20 atom % to 50atom % of nitrogen, 0 atom % to 20 atom %, specifically 0 atom % to 5atom % of carbon, and 0 atom % to 35 atom %, specifically 1 atom % to 20atom % of transition metal.

The antireflective film, when its composition is graded in a thicknessdirection, preferably has a composition consisting essentially of 0 atom% to 90 atom %, specifically 10 atom % to 90 atom % of silicon, 0 atom %to 67 atom %, specifically 5 atom % to 67 atom % of oxygen, 0 atom % to57 atom %, specifically 5 atom % to 50 atom % of nitrogen, 0 atom % to20 atom %, specifically 0 atom % to 5 atom % of carbon, and 0 atom % to95 atom %, specifically 1 atom % to 20 atom % of transition metal.

Further, a choice of compositional ratio of transition metal to siliconin the range from 1:4 to 1:15 (atomic ratio) advantageously enhances theinertness to chemicals used in cleaning and other purposes. Even whenthe compositional ratio of transition metal to silicon is outside therange, the inclusion of nitrogen, especially to a nitrogen content of 5atom % to 40 atom %, imparts the chemical inertness required and iseffective for alleviating damages during oxygen-containing chlorine dryetching for the etching of a Cr film used as the etching mask film. Atthis time, the ratio of transition metal to silicon may be in a rangefrom 1:1 to 1:10 (atomic ratio), for example.

The transition metal and silicon-containing material is required to havechemical stability in that its film undergoes little or no thicknesschange during cleaning. The photomask for ArF lithography is required tohave a film thickness change of up to 3 nm during cleaning. It isnecessary to avoid the situation that the conditions of cleaningrequisite in the photomask production process, especially cleaning withsulfuric acid/aqueous hydrogen peroxide, damage the light-shielding filmto deprive it of a light-shielding effect. Also the conductivity of thelight-shielding film should be controlled so as to prevent any chargebuildup upon exposure of electron beam in the lithographic process formask pattern formation.

The light-shielding film and antireflective film, when the molar ratioof transition metal to silicon is in the range from 1:4 to 1:15 (atomicratio), exhibit chemical resistance during rigorous chemical cleaningwithout a need for optimization of a nitrogen content as well as aconductivity within a practically acceptable range.

The materials which are resistant to fluorine dry etching of thelight-shielding film and antireflective film include chromium-basedmaterials, preferably chromium alone or chromium compounds containingchromium and at least one element selected from oxygen, nitrogen andcarbon, more preferably chromium compounds containing chromium andoxygen and/or nitrogen, and should preferably be free of silicon. Moreillustrative examples of the chromium compound include chromium oxide,chromium nitride, chromium oxynitride, chromium oxycarbide, chromiumnitride carbide, and chromium oxide nitride carbide.

With respect to the composition of chromium-based material, thelight-shielding film preferably has a composition consisting essentiallyof 50 atom % to 100 atom %, specifically 60 atom % to 100 atom % ofchromium, 0 atom % to 50 atom %, specifically 0 atom % to 40 atom % ofoxygen, 0 atom % to 50 atom %, specifically 0 atom % to 40 atom % ofnitrogen, and 0 atom % to 20 atom %, specifically 0 atom % to 10 atom %of carbon.

The light-shielding film, when its composition is graded in a thicknessdirection, preferably has a composition consisting essentially of 50atom % to 100 atom %, specifically 60 atom % to 100 atom % of chromium,0 atom % to 60 atom %, specifically 0 atom % to 50 atom % of oxygen, 0atom % to 50 atom %, specifically 0 atom % to 40 atom % of nitrogen, and0 atom % to 20 atom %, specifically 0 atom % to 10 atom % of carbon.

With respect to the composition of chromium compound, the antireflectivefilm preferably has a composition consisting essentially of 30 atom % to70 atom %, specifically 35 atom % to 50 atom % of chromium, 0 atom % to60 atom %, specifically 20 atom % to 60 atom % of oxygen, 0 atom % to 50atom %, specifically 3 atom % to 30 atom % of nitrogen, and 0 atom % to20 atom %, specifically 0 atom % to 5 atom % of carbon.

The antireflective film, when its composition is graded in a thicknessdirection, preferably has a composition consisting essentially of 30atom % to 100 atom %, specifically 35 atom % to 90 atom % of chromium, 0atom % to 60 atom %, specifically 3 atom % to 60 atom % of oxygen, 0atom % to 50 atom %, specifically 3 atom % to 50 atom % of nitrogen, and0 atom % to 30 atom %, specifically 0 atom % to 20 atom % of carbon.

The light-shielding film may consist of a single layer or multiplelayers or even a single layer with continuous compositional grading in athickness direction or multiple layers with stepwise compositionalgrading in a thickness direction including at least one layer containinga transition metal and silicon. In the case of multilayer construction,layers other than the transition metal and silicon-containing layerinclude a tungsten layer, tantalum layer or the like.

The light-shielding film preferably has a thickness of 10 to 80 nm.Although the exact thickness depends on the construction of thelight-shielding film, no sufficient light-shielding effect may beavailable at a thickness of less than 10 nm, and a film with a thicknessin excess of 80 nm may interfere with high-accuracy processing using athin resist film with a thickness equal to or less than 250 nm or causethe substrate to bow due to film stress. When an etching mask film isused as will be described later, a film thickness greater than the rangeis acceptable insofar as means for solving the problem of film stress isemployed.

The light-shielding film used herein is a film imparting alight-shielding effect to exposure light during use of the photomask andis not particularly limited. When the photomask blank is of the layerconstruction wherein when the photomask blank is processed into aphotomask, the light-shielding film mainly plays the light shieldingrole of the photomask, for example, it is a photomask blank wherein thelight-shielding film is disposed directly on the transparent substrateas illustrated in FIGS. 1A, 2A, 3A, 4A and 5A, or a photomask blankwherein the light-shielding film is disposed on the transparentsubstrate via a phase shift film as illustrated in FIGS. 1B, 2B, 3B, 4Band 5B, the phase shift film being of full transmission type, thecomposition and thickness of the light-shielding film are preferablyadjusted so that it may have an optical density of 1 to 4 relative tothe exposure light. In this case, the light-shielding film preferablyhas a thickness of 10 to 80 nm.

On the other hand, when the photomask blank is of the constructionwherein another film of mainly playing the light shielding role of thephotomask is present in addition to the light-shielding film, forexample, it is a photomask blank wherein the light-shielding film isdisposed on the transparent substrate via a phase shift film asillustrated in FIGS. 1B, 2B, 3B, 4B and 5B, the phase shift film being ahalftone phase shift film having a transmittance of exposure light ofabout 5% to about 30%, the composition and thickness of thelight-shielding film are preferably adjusted so that it may have anoptical density of 0.2 to 4 relative to the exposure light. In thiscase, the light-shielding film preferably has a thickness of 10 to 70nm.

The antireflective film of chromium-based material may function as anetching mask when a film susceptible to fluorine dry etching is etched.In this case, the antireflective film of chromium-based material ispreferably composed of chromium alone or a chromium compound containingchromium and at least one element selected from oxygen, nitrogen andcarbon, with a chromium content of at least 50 atom %. Then theantireflective film can exert an etching mask function effectivelywithout a need for thickness increase.

In order to function as an antireflective film, the material must havecertain levels of light transmission and absorption. Even metallicchromium or materials having a chromium content of more than 85 atom %can be used as a partial layer in the film if the layer is extremelythin. The design preferred for enhancing a mask function during etchingis a combination of a layer with a chromium content in excess of 50 atom% and a layer with a relatively low chromium content (e.g., equal to orless than 40 atom %) because the etching mask effect abruptly rises whenthe chromium content exceeds 50 atom %.

With respect to the thickness of the antireflective film used herein, anantireflection effect is generally obtained at a thickness in the rangeof 5 to 50 nm, preferably 10 to 30 nm, although the exact thicknessvaries with the wavelength of light used in inspection required in themanufacture or use of the photomask. A thickness in the range of 15 to25 nm is preferred especially for the ArF excimer laser lithography.

Either the light-shielding film or the antireflective film may bedeposited by well-known methods. The sputtering process is often usedbecause a homogeneous film can be formed most easily. The sputteringprocess is yet the preferred deposition process used herein. When a filmcontaining a transition metal and silicon is to be deposited, the targetused may be a single target containing silicon and transition metal in acontrolled ratio. Alternatively, a ratio of silicon to transition metalmay be adjusted by selecting appropriate ones from a silicon target, atransition metal target, and targets of silicon and transition metal(transition metal silicide targets) and controlling the sputtering areaof the selected targets or the power applied to the selected targets. Onthe other hand, when a film is formed of a chromium compound, a chromiumtarget may be used. It is noted that when the film contains lightelements such as oxygen, nitrogen, and carbon, such a film can bedeposited by reactive sputtering wherein an oxygen-containing gas,nitrogen-containing gas and/or carbon-containing gas is added to thesputtering gas as a reactive gas.

The photomask blank of the invention may be one comprising an etchingmask film of a single layer or multilayer structure which is depositedcontiguous to the antireflective film, resistant to fluorine dry etchingand removable by chlorine dry etching, as in the second embodiment. Theetching mask film functions as an etching mask during fluorine dryetching of the light-shielding film.

Particularly in the event the light-shielding film pattern is to be leftat a high accuracy on the phase shift pattern of the phase shift film ortransparent substrate, it must be etch processed while fully protectingthe antireflective film with a first resist film pattern formedinitially, so as to avoid any damages to the antireflective film. Thephase shifter is then processed using a second resist film pattern whichis formed after the first resist film pattern is stripped. Ifretrogression occurs due to damages by pattern-wise etching of thesecond resist film, a film affording light-shielding property lowers itsfunction.

For preventing this, the resist film must have high etching resistanceor be formed thick. However, in a practical sense, there is often atradeoff between imparting high etching resistance to the resist film orforming the resist film to an increased thickness and imparting a highresolution to the resist film to form a fine resist pattern. When theultimate mask pattern is required to have a micro-structure and a highaccuracy, the use of an etching mask film is preferred in some cases,though it makes the process complicated.

Like the etch stop film, the etching mask film has functions ofproviding certain resistance to fluorine dry etching and enablingselective etching relative to the material containing a transition metaland silicon. To enhance etching accuracy during the etching of the phaseshifter, the etching mask film must have greater resistance to fluorinedry etching. The preferred materials satisfying such requirements arechromium-based materials among other materials as exemplified for theetch stop film. When the etching mask film is used as an etching maskfor deep etching of the transparent substrate, as in the case ofLevenson masks and chromeless masks wherein the phase shifter is formedby etching the transparent substrate, chromium-based materials areespecially preferred because extremely high etching resistance isrequired for the etching mask film.

The desired chromium-based materials include chromium alone and chromiumcompounds containing chromium and at least one element selected fromoxygen, nitrogen and carbon and should preferably be free of silicon.More illustrative examples of the chromium compound include chromiumoxide, chromium nitride, chromium oxynitride, chromium oxycarbide,chromium nitride carbide, and chromium oxide nitride carbide.

An etching mask film is improved in etching resistance at a chromiumcontent of at least 50 atom %, especially at least 60 atom %, thoughdepending on the film thickness. Then using chromium alone or chromiumcompounds with a chromium content in the range, an etching mask filmwhich is expected to have a better etching mask effect can be formedwithout increasing the thickness of the film.

The chromium-based material has, for example, a composition consistingessentially of 50 atom % to 100 atom %, specifically 60 atom % to 100atom % of chromium, 0 atom % to 50 atom %, specifically 0 atom % to 40atom % of oxygen, 0 atom % to 50 atom %, specifically 0 atom % to 40atom % of nitrogen, and 0 atom % to 20 atom %, specifically 0 atom % to10 atom % of carbon. The chromium-based material having this compositioncan form an etching mask film having sufficient etching selectivityrelative to the light-shielding film and/or transparent substrate.

When the etching mask film is formed using the above material to athickness of about 2 to 30 nm, especially about 5 to 30 nm, it can beprocessed so as to acquire a satisfactory etching mask effect withoutraising the problem of pattern density dependency. This enhances theaccuracy of etch processing of the film underlying the etching mask filmand the transparent substrate.

The etching mask film used herein may have a single layer structure or amultilayer structure. The single layer structure simplifies the filmconstruction and the process reflective thereon.

Like the etch stop film, the etching mask film, which is formed frommetallic chromium or a chromium compound with a high chromium content,is sometimes short of the adhesion at the interface between the etchingmask film and a contiguous film of different material or the resist. Insuch cases, like the etch stop film, the etching mask film is tailoredby constructing a portion of the etching mask film which is contiguousto the antireflective film, or a portion of the etching mask film whichis contiguous to the resist film, that is, one or both of oppositesurface portions of the etching mask film in a thickness direction inthe case of single layer structure, and one or both of remotest layersof the etching mask film in a thickness direction in the case ofmultilayer structure, so as to have a higher oxygen and/or nitrogencontent than the region with the highest chromium content in a thicknessdirection. Then the adhesion to the antireflective film can be improvedto prevent occurrence of defects, or the adhesion to the resist film canbe improved to prevent the resist pattern from collapsing. Thesestructures can be readily formed by controlling the parameters ofreactive sputtering.

Notably, when the photomask blank has an etching mask film, it issometimes advantageous to establish selective etching between the etchstop film and the etching mask film. In this case, if the etching maskfilm is made of a chromium-based material and the etch stop film is madeof tantalum alone or a tantalum compound containing tantalum, free ofsilicon, then selective etching is possible between the etch stop filmand the etching mask film.

The etching mask film can be deposited by well-known methods. Thesputtering process is preferable and may be either DC sputtering, RFsputtering or the like.

The etching mask film may be deposited by a procedure used in the priorart for chromium-based light-shielding films and antireflective films.One commonly used method is by sputtering a chromium target in an inertgas such as argon, a reactive gas such as oxygen-containing gas,nitrogen-containing gas or carbon-containing gas, or a mixture of aninert gas and a reactive gas. See JP-A 7-140635, for example.

Described below are the photomask blanks of the third to fifthembodiments referred to above as the construction permitting thelight-shielding film and antireflective film to be processed by two dryetching steps.

The photomask blank of the third embodiment is expected to achieve thebest improvements over the problem of pattern density dependency arisingin forming a transferred pattern with a feature size equal to or lessthan 0.4 μm. In addition, the layer of the antireflective film which isdisposed remote from the transparent substrate (surface side layer) isformed of a material resistant to fluorine dry etching. If its etchingmask function is utilized during the processing step, the use of anetching mask film is not always needed. Then, the number of processingsteps can be reduced because the step of eventually removing the etchingmask film is omitted.

On the other hand, while the surface side layer of the antireflectivefilm is used as an etching mask, any underlying film (or layer) ortransparent substrate is etched to form a phase shifter. To this end,the antireflective film is constructed so as to contain more lightelements than films with better light-shielding effect of materials ofthe same family.

In the third embodiment, the surface side layer of the antireflectivefilm made of chromium-based material preferably has an atomiccomposition consisting essentially of 30 atom % to 70 atom %,specifically 35 atom % to 50 atom % of chromium, 0 atom % to 60 atom %,specifically 20 atom % to 60 atom % of oxygen, 0 atom % to 50 atom %,specifically 3 atom % to 30 atom % of nitrogen, and 0 atom % to 20 atom%, specifically 0 atom % to 5 atom % of carbon.

The surface side layer of the antireflective film, when its compositionis graded in a thickness direction, preferably has a compositionconsisting essentially of 30 atom % to 100 atom %, specifically 35 atom% to 90 atom % of chromium, 0 atom % to 60 atom %, specifically 3 atom %to 60 atom % of oxygen, 0 atom % to 50 atom %, specifically 3 atom % to50 atom % of nitrogen, and 0 atom % to 30 atom %, specifically 0 atom %to 20 atom % of carbon.

With respect to the thickness of the antireflective film used herein, anantireflection effect is generally obtained at an overall thickness inthe range of 10 to 30 nm, although the exact thickness varies with thewavelength of light used in inspection required in the manufacture oruse of the photomask. A thickness in the range of 15 to 25 nm ispreferred especially for the ArF excimer laser lithography.

The function of the antireflective film is exerted when a layersusceptible to fluorine dry etching (first antireflective layer) and alayer resistant to fluorine dry etching (second antireflective layer)cooperate together.

In this embodiment, the second antireflective layer has a thickness of 2to 25 nm, especially 2 to 20 nm, and the first antireflective layer hasa thickness corresponding to the balance of the overall thicknessdescribed above.

The photomask blank of the fourth embodiment is expected to achievebetter improvements over the problem of pattern density dependencyarising in forming a transferred pattern with a feature size equal to orless than 0.4 μm. In addition, the layer of the light-shielding filmwhich is disposed adjacent to the antireflective film and theantireflective film are formed of a material resistant to fluorine dryetching. If their etching mask function is utilized during theprocessing step, the use of an etching mask film is not always needed.Then, the number of processing steps can be reduced because the step ofeventually removing the etching mask film is omitted.

On the other hand, while the layer of the light-shielding film which isdisposed adjacent to the antireflective film and the antireflective filmare used as an etching mask, any underlying film (or layer) ortransparent substrate is etched to form a phase shifter. If the resistfilm is retrogressed by damages during the step, the antireflective filmis also damaged. In such a situation, the layer of the light-shieldingfilm which is disposed adjacent to the antireflective film is tailoredto a relatively low content of light elements, whereby the etching maskfunction is enhanced as compared with the use of a material resistant tofluorine dry etching only in the antireflective film.

In the fourth embodiment, the antireflective film made of chromium-basedmaterial preferably has an atomic composition consisting essentially of30 atom % to 85 atom % of chromium, 0 atom % to 60 atom % of oxygen, 0atom % to 50 atom % of nitrogen, and 0 atom % to 20 atom % of carbon.The antireflective film preferably has a thickness of at least 5 nm whena relatively intense etching mask function is required. It alsopreferably has a thickness of up to 50 nm because the effect ofimproving pattern density dependency is extremely weakened at athickness in excess of 50 nm.

The photomask blank of the fifth embodiment is expected to achieveimprovements over the problem of pattern density dependency arising informing a transferred pattern with a feature size equal to or less than0.4 μm. In addition, the antireflective film is formed of a materialresistant to fluorine dry etching. If its etching mask function isutilized during the processing step, the use of an etching mask film isnot always needed. Then, the number of processing steps can be reducedbecause the step of eventually removing the etching mask film isomitted.

While the antireflective film is used as an etching mask, any underlyingfilm (or layer) or transparent substrate is etched to form a phaseshifter. To this end, the antireflective film is constructed so as tocontain more light elements than films with better light-shieldingeffect of materials of the same family.

In the fifth embodiment, the antireflective film made of chromium-basedmaterial preferably has an atomic composition consisting essentially of30 atom % to 95 atom % of chromium, 0 atom % to 60 atom % of oxygen, 0atom % to 50 atom % of nitrogen, and 0 atom % to 20 atom % of carbon.

With respect to the thickness of the antireflective film used herein, anantireflection effect is generally obtained at a thickness in the rangeof 15 to 30 nm, although the exact thickness varies with the wavelengthof light used in inspection required in the manufacture or use of thephotomask. A thickness in the range of 20 to 25 nm is preferredespecially for the ArF excimer laser lithography.

In this embodiment, the second light-shielding layer has a thickness of2 to 55 nm, especially 2 to 30 nm, and the first light-shielding layerhas a thickness corresponding to the balance of the overall thickness ofthe light-shielding film described above.

As viewed from the standpoint of etching resistance, each of thelight-shielding film and the antireflective film in the photomask blanksof the third to fifth embodiments is constructed from a lower sectionsusceptible to fluorine dry etching and an upper section resistant tofluorine dry etching and removable by chlorine dry etching. In the thirdembodiment, the light-shielding film and first antireflective layercorrespond to the lower section, and the second antireflective layercorresponds to the upper section. In the fourth embodiment, thelight-shielding film corresponds to the lower section, and theantireflective film corresponds to the upper section. In the fifthembodiment, the first light-shielding layer corresponds to the lowersection, and the antireflective film and second light-shielding layercorrespond to the upper section. Accordingly, in processing thephotomask blanks of the third to fifth embodiments into photomasks, ahalftone phase shift mask (tritone phase shift mask), chromeless maskand Levenson mask can be individually produced by applying a commonetching procedure.

In the photomask blank of the invention, in order that films havinglight-shielding property deposited on the transparent substrate (whichcorrespond to a light-shielding film, an etch stop film impartingcomplementary light-shielding property (an etch stop film of a certaintype can impart complementary light-shielding property), anantireflective film imparting complementary light-shielding property (anantireflective film of a certain type can impart complementarylight-shielding property), a halftone phase shift film or the like)function as a whole to provide sufficient light-shielding property, thephotomask blank should desirably be processed into a photomask in whichthe films having light-shielding property have an overall opticaldensity OD of 1.0 to 3.5 relative to exposure light during use of thephotomask.

Also, the combination of light-shielding film, antireflective film andetch stop film, and if a halftone phase shift film is used together, thecombination of etching mask film, light-shielding film, antireflectivefilm, etch stop film, and halftone phase shift film should preferablyhave an optical density OD of at least 2.5, more preferably at least2.8, and even more preferably at least 3.0.

For the light-shielding film containing light elements such as oxygen,nitrogen and carbon, in particular, sufficient light-shielding propertymay not be obtained when the content of light elements exceeds a certainlevel. When the photomask blank of the invention is adapted for exposureto light with a wavelength equal to or less than 193 nm (to which theinvention is advantageously applied), for example, exposure to ArFexcimer laser with a wavelength 193 nm, or exposure to F₂ laser with awavelength 153 nm, it is preferred that the light-shielding film have anitrogen content of up to 20 atom %, a carbon content of up to 20 atom%, an oxygen content of up to 10 atom %, and especially a total contentof nitrogen, carbon and oxygen of up to 40 atom %. Satisfactory lightshielding property is obtained when at least a portion, preferably theentirety of the light-shielding film has a composition within the range.

The transparent substrate is preferably selected from substratescomposed mainly of silicon oxide, typically quartz substrates. When aphase shift film is used, it may be either a full transmission phaseshift film or a halftone phase shift film, for example, a halftone phaseshift film having a transmittance of 5 to 30%. The phase shift film usedherein is preferably a film which can be etched by fluorine dry etching.Examples of the material of which the phase shift film is made includesilicon-containing materials, preferably transition metal siliconcompounds containing a transition metal, silicon and at least oneelement selected from oxygen, nitrogen and carbon, more preferablytransition metal silicon compounds containing a transition metal,silicon and at least one of nitrogen and oxygen. Examples of thesilicon-containing material are as exemplified above as thesilicon-containing compound for the light-shielding film; and examplesof the transition metal are as exemplified above as the transition metalfor the light-shielding film. The phase shift film has a thickness whichis selected so as to shift the phase of light by a predeterminedquantity, typically 180° relative to the exposure light during the useof the photomask.

The phase shift film can be deposited by well-known methods. Amongothers, the sputtering process is preferable because a homogeneous filmcan be formed most easily. The sputtering process may be either DCsputtering, RF sputtering or the like.

The target and sputtering gas are selected in accordance with thedesired film composition. When a phase shift film containing atransition metal and silicon is formed, the target used may be a singletarget containing silicon and transition metal in a controlled ratio.Alternatively, a ratio of silicon to transition metal may be adjusted byselecting appropriate ones from a silicon target, a transition metaltarget, and targets of silicon and transition metal (transition metalsilicide targets) and controlling the sputtering area of the selectedtargets or the power applied to the selected targets. It is noted thatwhen the film contains light elements such as oxygen, nitrogen, andcarbon, such a film can be deposited by reactive sputtering wherein anoxygen-containing gas, nitrogen-containing gas and/or carbon-containinggas is added to the sputtering gas as a reactive gas.

According to the invention, a photomask is obtained from theabove-described photomask blank by patterning the respective films ofthe blank as desired by fluorine dry etching and chlorine dry etching ina proper combination, for forming on the transparent substrate a maskpattern including transparent regions and effectively opaque regions toexposure light.

As used in the context that a certain material or layer is susceptibleto fluorine dry etching, the term “fluorine dry etching” refers to dryetching using a fluorine-containing gas. The fluorine-containing gas maybe any gas containing fluorine element, specifically fluorine gas, gasescontaining carbon and fluorine such as CF₄ and C₂F₆, gases containingsulfur and fluorine such as SF₆, or a mixture of a fluorine-free gassuch as helium and a fluorine-containing gas. Other gases such as oxygenmay be added thereto if necessary.

As used in the context that a certain material or layer is resistant tofluorine dry etching and removable by chlorine dry etching, the term“chlorine dry etching” refers to dry etching using a chlorine-containinggas. Chlorine dry etching conditions are well known for the dry etchingof chromium compound films and not particularly limited. For example,the etchant gas is a mixture of chlorine gas and oxygen gas in a volumeflow rate ratio (Cl₂ gas:O₂ gas) of 1:2 to 20:1, optionally in admixturewith an inert gas such as helium. When oxygen gas is admixed at a volumeflow rate ratio of at least 5% relative to the chlorine gas, nosubstantial etching takes place on the transition metal andsilicon-containing materials of which the light-shielding film andantireflective film are formed and the transparent substrate in thephotomask blank of the invention.

Referring to the drawings, the processes of manufacturing photomasksfrom the photomask blanks of the first to fifth embodiments aredescribed in detail.

(1) The Photomask Manufacturing Process A Wherein the Photomask Blank ofthe First Embodiment is Processed Into a Photomask (Levenson Mask)

The process starts with a photomask blank comprising an etch stop film 9resistant to fluorine dry etching and removable by chlorine dry etching,a light-shielding film 2 susceptible to fluorine dry etching, and anantireflective film 3 susceptible to fluorine dry etching, deposited ona transparent substrate 1 in the described sequence (FIG. 1A). A firstresist film 6 is coated onto the blank (FIG. 6A) and then developed toform a pattern of first resist film 6 corresponding to the configurationof a portion of light-shielding film 2 to be left (FIG. 6B). With thepattern of first resist film 6 serving as an etching mask, fluorine dryetching is then performed for transferring the pattern of first resistfilm 6 to the antireflective film 3 and light-shielding film 2 (FIG.6C). Further etch stop film 9 is etched by chlorine dry etching (dryetching with chlorine and oxygen). All the portions of the respectivefilms to be removed are removed without damages to the transparentsubstrate (FIG. 6D).

Once first resist film 6 is stripped, a second resist film 7 is coatedagain. The second resist film 7 is processed into a pattern thatprotects the area where light-shielding film 2 is to be left and thearea where transparent substrate 1 is not to be etched among the areawhere light-shielding film 2 has been removed (FIG. 6E). By fluorine dryetching, the area of transparent substrate 1 to be processed (the areawhere second resist film 7 has been removed) is etched to apredetermined depth. This forms a phase shifter in transparent substrate1 (FIG. 6F). Finally, second resist film 7 is removed, completing aLevenson mask (FIG. 6G).

(2) The Photomask Manufacturing Process B Wherein the Photomask Blank ofthe First Embodiment is Processed Into a Photomask (Halftone Phase ShiftMask or Tritone Phase Shift Mask)

The process starts with a photomask blank comprising a halftone phaseshift film 8 susceptible to fluorine dry etching, an etch stop film 9resistant to fluorine dry etching and removable by chlorine dry etching,a light-shielding film 2 susceptible to fluorine dry etching, and anantireflective film 3 susceptible to fluorine dry etching, deposited ona transparent substrate 1 in the described sequence (FIG. 1B). A firstresist film 6 is coated onto the blank (FIG. 7A) and then processed toform a pattern of first resist film 6 corresponding to the configurationof a portion of halftone phase shift film 8 to be left (FIG. 7B). Withthe pattern of first resist film 6 serving as an etching mask, fluorinedry etching is then performed for transferring the pattern of firstresist film 6 to antireflective film 3 and light-shielding film 2 (FIG.7C). Further etch stop film 9 is etched by chlorine dry etching (dryetching with chlorine and oxygen), forming an opening at the area wherehalftone phase shift film 8 is to be removed (FIG. 7D).

Once first resist film 6 is stripped, a second resist film 7 is coatedagain. The second resist film 7 is processed into a pattern at the areawhere light-shielding film 2 is to be left, protecting light-shieldingfilm 2 and antireflective film 3 (FIG. 7E). Fluorine dry etching is thenperformed, whereby a portion of halftone phase shift film 8 to beremoved (in register with the opening in etch stop film 9) is removedand those portions of antireflective film 3 and light-shielding film 2which are not protected by second resist film 7 are removed (FIG. 7F).Thereafter, chlorine dry etching (dry etching with chlorine and oxygen)is performed again, whereby the portion of etch stop film 9 which is notprotected by second resist film 7 (the portion exposed after removal oflight-shielding film 2) is removed (FIG. 7G). All the portions of therespective films to be removed are removed without damages totransparent substrate 1 and halftone phase shift film 8 (FIG. 7H).

If it is desired to leave a portion of the light-shielding film only atthe light-shielding band (usually photomask periphery), the process maybe modified such that after the antireflective film and light-shieldingfilm are etched through the pattern of the first resist film, only thelight-shielding band is protected by the second resist film. Thesubsequent steps are the same. By this modification, a general halftonephase shift mask is produced.

(3) The Photomask Manufacturing Process C Wherein the Photomask Blank ofthe Second Embodiment is Processed Into a Photomask (Levenson Mask)

An exemplary procedure of processing a photomask blank having an etchingmask film into a Levenson mask is described.

The process starts with a photomask blank comprising an etch stop film 9resistant to fluorine dry etching and removable by chlorine dry etching,a light-shielding film 2 susceptible to fluorine dry etching, anantireflective film 3 susceptible to fluorine dry etching, and anetching mask film 4 resistant to fluorine dry etching and removable bychlorine dry etching, deposited on a transparent substrate 1 in thedescribed sequence (FIG. 2A). A first resist film 6 is coated onto theblank (FIG. 8A) and then developed to form a pattern of first resistfilm 6 corresponding to the configuration of a portion oflight-shielding film 2 to be left (FIG. 8B). With the pattern of firstresist film 6 serving as an etching mask, chlorine dry etching (dryetching with chlorine and oxygen) is then performed for transferring thepattern of first resist film 6 to etching mask film 4 (FIG. 8C).Fluorine dry etching is then performed for transferring the pattern ofetching mask film 4 to antireflective film 3 and light-shielding film 2(FIG. 8D). Further etch stop film 9 is etched by chlorine dry etching(dry etching with chlorine and oxygen). All the portions of therespective films to be removed are removed without damages totransparent substrate 1 (FIG. 8E).

Once first resist film 6 is stripped, a second resist film 7 is coatedagain. The second resist film 7 is processed into a pattern thatprotects the area where light-shielding film 2 is to be left and thearea where transparent substrate 1 is not to be etched among the areawhere light-shielding film 2 has been removed (FIG. 8F). By fluorine dryetching, the area of transparent substrate 1 to be processed (the areawhere second resist film 7 has been removed) is etched to apredetermined depth. This forms a phase shifter in transparent substrate1 (FIG. 8G). Finally, second resist film 7 is removed, completing aLevenson mask (FIG. 8H).

(4) The Photomask Manufacturing Process D Wherein the Photomask Blank ofthe Second Embodiment is Processed Into a Photomask (Zebra TypeChromeless Mask)

The film arrangement like the photomask blank of the second embodimentexerts its effect to a full extent when the blank is processed into amask having a more complex light-shielding film pattern formed on theprocessed phase shift film, for example, a zebra type chromeless mask.Described below is one exemplary process toward a zebra type chromelessmask.

The process starts with a photomask blank comprising an etch stop film 9resistant to fluorine dry etching and removable by chlorine dry etching,a light-shielding film 2 susceptible to fluorine dry etching, anantireflective film 3 susceptible to fluorine dry etching, and anetching mask film 4 resistant to fluorine dry etching and removable bychlorine dry etching, deposited on a transparent substrate 1 in thedescribed sequence (FIG. 2A). A first resist film 6 is coated onto theblank (FIGS. 9A, 9B) and then developed to form a pattern of firstresist film 6 which is open where transparent substrate 1 is to be dug(FIGS. 9C, 9D). With the pattern of first resist film 6 serving as anetching mask, chlorine dry etching (dry etching with chlorine andoxygen) is then performed for transferring the pattern of first resistfilm 6 to etching mask film 4 (FIGS. 9E, 9F). Fluorine dry etching isthen performed to etch away those portions of antireflective film 3 andlight-shielding film 2 within the openings in etching mask film 4 (FIGS.9G, 9H). By further chlorine dry etching (dry etching with chlorine andoxygen), etch stop film 9 is etched (FIGS. 9I, 9J).

Once first resist film 6 is stripped, a second resist film 7 is coatedagain. The second resist film 7 is processed into a pattern thatcorresponds to the configuration of a portion of light-shielding film 2to be left (FIGS. 10A, 10B). Notably, in the event the pattern of secondresist film 7 is an extremely fine dot pattern, since the portion oftransparent substrate 1 which has already been exposed is not a portionsubject to etching through the pattern of second resist film 7, thepattern of second resist film 7 may be intentionally formed so as tooverride this portion for preventing the fine dot pattern of secondresist film 7 from collapsing. Next, with the pattern of second resistfilm 7 serving as an etching mask, chlorine dry etching (dry etchingwith chlorine and oxygen) is performed, thereby removing a portion ofetching mask film 4 corresponding to the area where light-shielding film3 will be removed, but transparent substrate 1 will not be dug (FIGS.10C, 10D).

Thereafter, second resist film 7 is stripped (FIGS. 10E, 10F). Byfluorine dry etching, transparent substrate 1 is etched to apredetermined depth. This forms a phase shifter in transparent substrate1, and removes those portions of antireflective film 3 andlight-shielding film 2 corresponding to the portion of etching mask film4 which has been removed during the etching step using the pattern ofsecond resist film 7, with only etch stop film 9 being left at that area(FIGS. 10G, 10H). Finally, chlorine dry etching (dry etching withchlorine and oxygen) is performed for removing the exposed portion ofetch stop film 9 and the unremoved portion of etching mask film 4overlying antireflective film 3 on light-shielding film 2 at the sametime, completing a phase shift mask (zebra type chromeless mask) (FIGS.10I, 10J).

(5) The Photomask Manufacturing Process E Wherein the Photomask Blank ofthe Second Embodiment is Processed Into a Photomask (Halftone PhaseShift Mask or Tritone Phase Shift Mask)

The process starts with a photomask blank comprising a halftone phaseshift film 8 susceptible to fluorine dry etching, an etch stop film 9resistant to fluorine dry etching and removable by chlorine dry etching,a light-shielding film 2 susceptible to fluorine dry etching, anantireflective film 3 susceptible to fluorine dry etching, and anetching mask film 4 resistant to fluorine dry etching and removable bychlorine dry etching, deposited on a transparent substrate 1 in thedescribed sequence (FIG. 2B). A first resist film 6 is coated onto theblank (FIG. 11A) and then developed to form a pattern of first resistfilm 6 corresponding to the configuration of a portion of halftone phaseshift film 8 to be left (FIG. 11B). With the pattern of first resistfilm 6 serving as an etching mask, chlorine dry etching (dry etchingwith chlorine and oxygen) is then performed for transferring the patternof first resist film 6 to etching mask film 4 (FIG. 11C). Fluorine dryetching is then performed for transferring the pattern of first resistfilm 6 to antireflective film 3 and light-shielding film 2 (FIG. 11D).

Once first resist film 6 is stripped, a second resist film 7 is coatedagain. The second resist film 7 is processed into a pattern thatcorresponds to the configuration of a portion of light-shielding film 2to be left, for protecting the area of etching mask film 4 wherelight-shielding film 2 is to be left (FIG. 11E). Chlorine dry etching(dry etching with chlorine and oxygen) is then performed, whereby etchstop film 9 is etched, forming openings in the area where halftone phaseshift film 8 is to be removed, and etching mask film 4 in the area wherelight-shielding film 2 is to be removed is removed (FIG. 11F). Fluorinedry etching is then performed, whereby those portions of halftone phaseshift film 8 to be removed (in register with the openings in etch stopfilm 9) are removed, and those portions of antireflective film 3 andlight-shielding film 2 which are not protected by second resist film 7are removed (FIG. 11G). Then second resist film 7 is stripped, andchlorine dry etching (dry etching with chlorine and oxygen) is performedagain, for removing the portion of etch stop film 9 which is left in thearea where light-shielding film 2 is to be removed, and the unremovedportion of etching mask film 4 overlying the antireflective film 3 onlight-shielding film 2 at the same time. All the portions of therespective films to be removed are removed without damages totransparent substrate 1 and halftone phase shift film 8, completing atritone phase shift mask (FIG. 11H).

(6) The Photomask Manufacturing Process F Wherein the Photomask Blank ofthe Third Embodiment is Processed Into a Photomask (Levenson Mask)

The process starts with a photomask blank comprising an etch stop film 9resistant to fluorine dry etching and removable by chlorine dry etching,a light-shielding film 2 susceptible to fluorine dry etching, and anantireflective film 30 including a first antireflective layer 31susceptible to fluorine dry etching and a second antireflective layer 51resistant to fluorine dry etching, deposited on a transparent substrate1 in the described sequence (FIG. 3A). A first resist film 6 is coatedonto the blank (FIG. 12A) and then developed to form a pattern of firstresist film 6 corresponding to the shape of a portion of light-shieldingfilm 2 to be left (FIG. 12B). With the pattern of first resist film 6serving as an etching mask, chlorine dry etching (dry etching withchlorine and oxygen) is then performed for transferring the pattern offirst resist film 6 to second antireflective layer 51 (FIG. 12C).Fluorine dry etching is then performed for transferring the pattern ofsecond antireflective layer 51 to first antireflective layer 31 andlight-shielding film 2 (FIG. 12D). Further etch stop film 9 is etched bychlorine dry etching (dry etching with chlorine and oxygen). All theportions of the respective films to be removed are removed withoutdamages to the transparent substrate (FIG. 12E).

Once first resist film 6 is stripped, a second resist film 7 is coatedagain. The second resist film 7 is processed into a pattern thatprotects the area where light-shielding film 2 is to be left and thearea where transparent substrate 1 is not to be etched among the areawhere light-shielding film 2 has been removed (FIG. 12F). By fluorinedry etching, the area of transparent substrate 1 to be processed (thearea where second resist film 7 has been removed) is etched to apredetermined depth. This forms a phase shifter in transparent substrate1 (FIG. 12G). Finally, second resist film 7 is removed, completing aLevenson mask (FIG. 12H).

(7) The Photomask Manufacturing Process G Wherein the Photomask Blank ofthe Third Embodiment is Processed Into a Photomask (Halftone Phase ShiftMask or Tritone Phase Shift Mask)

The process starts with a photomask blank comprising a halftone phaseshift film 8 susceptible to fluorine dry etching, an etch stop film 9resistant to fluorine dry etching and removable by chlorine dry etching,a light-shielding film 2 susceptible to fluorine dry etching, and anantireflective film 30 including a first antireflective layer 31susceptible to fluorine dry etching and a second antireflective layer 51resistant to fluorine dry etching, deposited on a transparent substrate1 in the described sequence (FIG. 3B). A first resist film 6 is coatedonto the blank (FIG. 13A) and then developed to form a pattern of firstresist film 6 corresponding to the shape of a portion of phase shiftfilm 8 to be left (FIG. 13B). With the pattern of first resist film 6serving as an etching mask, chlorine dry etching (dry etching withchlorine and oxygen) is then performed for transferring the pattern offirst resist film 6 to second antireflective layer 51 (FIG. 13C).Fluorine dry etching is then performed for transferring the pattern ofsecond antireflective layer 51 to first antireflective layer 31 andlight-shielding film 2 (FIG. 13D).

Once first resist film 6 is stripped, a second resist film 7 is coatedagain. The second resist film 7 is processed into a patterncorresponding to the portion of light-shielding film 2 to be left,protecting second antireflective layer 51 in the area wherelight-shielding film 2 is to be left (FIG. 13E). By chlorine dry etching(dry etching with chlorine and oxygen), etch stop film 9 is etched forforming openings in the area where halftone phase shift film 8 is to beremoved and removing second antireflective layer 51 in the area wherelight-shielding film 2 is to be removed (FIG. 13F). Fluorine dry etchingis then performed, whereby the portion of halftone phase shift film 8 tobe removed (in register with the openings in second antireflective layer51) is removed and those portions of first antireflective layer 31 andlight-shielding film 2 which are not protected by second resist film 7and second antireflective layer 51 are removed (FIG. 13G). Thereafter,chlorine dry etching (dry etching with chlorine and oxygen) is performedagain, removing the portion of etch stop film 9 which has been left inthe area where light-shielding film 2 is to be removed. All the portionsof the respective films to be removed are removed without damages totransparent substrate 1 and halftone phase shift film 8. Finally, thepattern of second resist film 7 is removed, completing a tritone phaseshift mask (FIG. 13H).

If it is desired to leave a portion of the light-shielding film only atthe light-shielding band (usually photomask periphery), the process maybe modified such that after the antireflective film and light-shieldingfilm are etched through the pattern of the first resist film, only thelight-shielding band is protected by the second resist film. Thesubsequent steps are the same. By this modification, a general halftonephase shift mask is produced.

For photomasks in which a finally remaining light-shielding film patternneed not have a high accuracy, for example, general halftone phase shiftmasks in which a portion of the light-shielding film is left only at thelight-shielding band (usually photomask periphery), it suffices that atleast the phase shifter be processed at a high accuracy. In such a case,the use of the photomask blank of the third embodiment allows forprocessing even when the first resist film is considerably thin. Thereason is that once a predetermined portion of the second antireflectivelayer is accurately etched through the first resist film, any underlyinglayer (or film) can be processed using the overlying layer (or film) asan etching mask.

It is sometimes observed that as the resist film becomes thicker, theaspect ratio of the resist pattern increases to induce degradation ofthe resolving capability of the resist. The photomask blank of the thirdembodiment is most effective for solving this problem because processingis possible even when the thickness of the first resist film isconsiderably thin, for example, as thin as 200 nm or less, and even ofthe order of 100 nm, when a chemically amplified resist comprising aresin derived mainly from a hydroxystyrene skeleton component is used.

Understandably, in the third embodiment, the antireflective film ofchromium-based material, whose composition is determined so that itfunctions as an antireflective film, receives more damages by fluorinedry etching, as compared with the use of the etching mask film. It isthen necessary to set the resist film at a necessary thickness duringlithography using the second resist.

It is also possible to produce a zebra type chromeless mask from thephotomask blank of the third embodiment. The production process involvesa dry etching step using as an etching mask the surface layer of theoutermost antireflective layer which is not protected by the resist. Inview of the above-described characteristics of the antireflective filmof chromium-based material, the constituent films of the photomask blankmust be designed while taking into account the amount of theantireflective film which is lost during the step.

(8) The Photomask Manufacturing Process H Wherein the Photomask Blank ofthe Fourth Embodiment is Processed Into a Photomask (Halftone PhaseShift Mask)

The process starts with a photomask blank comprising a halftone phaseshift film 8 susceptible to fluorine dry etching, an etch stop film 9resistant to fluorine dry etching and removable by chlorine dry etching,a light-shielding film 2 susceptible to fluorine dry etching, and anantireflective film 5 resistant to fluorine dry etching and removable bychlorine dry etching, deposited on a transparent substrate 1 in thedescribed sequence (FIG. 4B). A first resist film 6 is coated onto theblank (FIG. 14A) and then processed to form a pattern of first resistfilm 6 corresponding to the configuration of a portion of halftone phaseshift film 8 to be left (FIG. 14B). With the pattern of first resistfilm 6 serving as an etching mask, chlorine dry etching (dry etchingwith chlorine and oxygen) is then performed for transferring the patternof first resist film 6 to antireflective film 5 (FIG. 14C). Fluorine dryetching is then performed for transferring the pattern of antireflectivefilm 5 to light-shielding film 2 (FIG. 14D).

Once first resist film 6 is stripped, a second resist film 7 is coatedagain. The second resist film 7 is processed into a patterncorresponding to the portion of light-shielding film 2 to be left,protecting antireflective film 5 in the area where light-shielding film2 is to be left (FIG. 14E). By chlorine dry etching (dry etching withchlorine and oxygen), etch stop film 9 is etched for forming openings inthe area where halftone phase shift film 8 is to be removed and removingantireflective film 5 in the area where the pattern of second resistfilm 7 is not formed (FIG. 14F). Fluorine dry etching is then performed,whereby the portion of halftone phase shift film 8 to be removed (inregister with the openings in etch stop film 9) is removed and thoseportions of light-shielding film 2 which are exposed after removal ofantireflective film 5 by etching through the pattern of second resistfilm 7 (FIG. 14G). Thereafter, chlorine dry etching (dry etching withchlorine and oxygen) is performed again, removing the portion of etchstop film 9 which is exposed after removal of light-shielding film 2.All the portions of the respective films to be removed are removedwithout damages to transparent substrate 1 and halftone phase shift film8. Finally, second resist film 7 is removed, completing a halftone phaseshift mask (FIG. 14H).

Since the photomask blank of the fourth embodiment has similar etchingcharacteristics to the photomask blank of the third embodiment, atritone phase shift mask or Levenson mask may be produced by the sameprocedure as in the photomask blank of the third embodiment. In thephotomask blank of the fourth embodiment, etch processing is possiblewith a resist film having a thickness of up to 250 nm. On the otherhand, an increased thickness of an antireflective film resistant tofluorine dry etching deposited on a light-shielding film susceptible tofluorine dry etching ensures masking during subsequent etching stepseven if the resist film is damaged in transferring the pattern of thefirst resist film. This increases the accuracy of pattern transfer toany film underlying the antireflective film and the transparentsubstrate.

(9) The Photomask Manufacturing Process I Wherein the Photomask Blank ofthe Fifth Embodiment is Processed Into a Photomask (Halftone Phase ShiftMask)

The process starts with a photomask blank comprising a halftone phaseshift film 8 susceptible to fluorine dry etching, an etch stop film 9resistant to fluorine dry etching and removable by chlorine dry etching,a light-shielding film 20 including a first light-shielding layer 21susceptible to fluorine dry etching and a second light-shielding layer22 resistant to fluorine dry etching, and an antireflective film 5resistant to fluorine dry etching, deposited on a transparent substrate1 in the described sequence (FIG. 5B). A first resist film 6 is coatedonto the blank (FIG. 15A) and then developed to form a pattern of firstresist film 6 corresponding to the configuration of a portion ofhalftone phase shift film 8 to be left (FIG. 15B). With the pattern offirst resist film 6 serving as an etching mask, chlorine dry etching(dry etching with chlorine and oxygen) is then performed fortransferring the pattern of first resist film 6 to antireflective film 5and second light-shielding layer 22 (FIG. 15C). Fluorine dry etching isthen performed for transferring the pattern of second light-shieldinglayer 22 to first light-shielding layer 21 (FIG. 15D).

Once first resist film 6 is stripped, a second resist film 7 is coatedagain. The second resist film 7 is processed into a patterncorresponding to the portion of light-shielding film 20 to be left,protecting antireflective film 5 in the area where light-shielding film20 is to be left (FIG. 15E). By chlorine dry etching (dry etching withchlorine and oxygen), etch stop film 9 is etched for forming openings inthe area where halftone phase shift film 8 is to be removed and removingantireflective film 5 in the area where light-shielding film 20 is to beremoved and second light-shielding layer 22 (FIG. 15F). Fluorine dryetching is then performed, whereby the portion of halftone phase shiftfilm 8 to be removed (in register with the openings in secondlight-shielding layer 22) is removed and those portions of firstlight-shielding layer 21 which are not protected by second resist film7, antireflective film 5 and second light-shielding layer 22 (FIG. 15G).Thereafter, chlorine dry etching (dry etching with chlorine and oxygen)is performed again, removing the portion of etch stop film 9 which isleft in the area where light-shielding film 2 is to be removed. All theportions of the respective films to be removed are removed withoutdamages to transparent substrate 1 and halftone phase shift film 8.Finally, the pattern of second resist film 7 is stripped, completing ahalftone phase shift mask (FIG. 15H).

Since the photomask blank of the fifth embodiment has similar etchingcharacteristics to the photomask blank of the third embodiment, atritone phase shift mask or Levenson mask may be produced by the sameprocedure as in the photomask blank of the third embodiment. In thephotomask blank of the fifth embodiment, the second light-shieldinglayer is expected to exert a greater etching mask effect. Even if theresist film is damaged in transferring the pattern of the first resistfilm, this ensures pattern transfer at a high accuracy to any film (orlayer) underlying the second light-shielding layer and the transparentsubstrate.

It is noted that the resist used in the manufacture of photomasksaccording to the invention may be either a negative resist or a positiveresist. A choice of a particular resist depends on the efficiency ofdistribution of a mask pattern.

EXAMPLE

Experiments and Examples are given below for further illustrating theinvention although the invention is not limited thereto.

In Examples, fluorine dry etching was performed by feeding only C₂F₆ gasinto a chamber at a flow rate of 20 sccm, and setting a pressure of 2 Pain the chamber. Chlorine dry etching is performed by feeding chlorinegas at a flow rate of 20 sccm, oxygen gas at 20 sccm and helium gas at80 sccm into a chamber, and setting a pressure of 2 Pa in the chamber.

Experiment 1

By selecting one of targets containing molybdenum and silicon in anatomic ratio of 0:100, 1:15, 1:9, 1:4, 1:2, and 1:1 and sputtering thetarget in an argon atmosphere, a molybdenum silicide film of 39 nm thickwas deposited (the film having a molybdenum/silicon ratio correspondingto the selected target). The molybdenum silicide films were immersed inaqueous ammonia/hydrogen peroxide (aqueous ammonia:hydrogenperoxide:water=1:1:30 in volume ratio) for one hour, after which achange of film thickness was determined. The film thickness losses were0.2, 0.2, 0.7, 1.5, 17.7, and 39 nm, respectively. The films were alsomeasured for electric conductivity using a four-probe sheet resistancemeter MCP-T600 (Mitsubishi Chemical Co., Ltd.), finding conductivityvalues of 1082, 680, 486, 296, 96, and 38 ohm/square (Ω/□),respectively.

With regard to these materials for light-shielding film andantireflective film (ARF), it was found that when the ratio oftransition metal to silicon is in a range from 1:4 to 1:15 in atomicratio, the resulting films have chemical resistance against intensechemical cleaning and an electric conductivity within a practicallyacceptable range, without a need for optimization of a nitrogen contentor the like.

Example 1

A photomask blank having the layer arrangement shown in FIG. 1A wasprepared by depositing the films by sputtering. The respective films areas follows.

-   Transparent substrate: quartz substrate-   Etch stop film: CrN (Cr:N=9:1 in atomic ratio, thickness 10 nm)-   Light-shielding film: MoSi (Mo:Si=1:4 in atomic ratio, thickness 41    nm)-   ARF: MoSiN (thickness-wise compositional grading from    Mo:Si:N=1:3:1.5 in atomic ratio on light-shielding film side to    Mo:Si:N=1:5:5 in atomic ratio on side remote from transparent    substrate (surface side), thickness 18 nm)

This photomask blank was processed in accordance with photomaskmanufacturing process A, whereby a Levenson mask was produced. For thefirst and second resist films, a chemically amplified negative resistmainly comprising a hydroxystyrene resin, a crosslinker, and a photoacidgenerator was used to form a resist film of 250 nm thick. The resistfilms were patterned by EB lithography. Before formation of the firstresist film, the surface of the photomask, specifically the surface ofthe antireflective film was treated with hexamethyl disilazane (HMDS).The phase shifter formed in the transparent substrate had a depth of 172nm, which produces a phase shift of about 180°.

As a result, a photomask which faithfully reflected the preselectedpattern size was produced independent of pattern density. It wasdemonstrated that the photomask blank has minimal pattern densitydependency. Since no erosion occurred on the substrate during etching ofthe light-shielding film, a phase shifter having the predetermined valueof phase shift could be formed in the substrate at a high accuracy.

Examples 2 and 3

Photomask blanks having the layer arrangement shown in FIG. 1A wereprepared as in Example 1 except that the light-shielding film was ofMoSiN having a nitrogen content of 5 atom % (Mo:Si:N=1:3:0.2 in atomicratio, thickness 23 nm) in Example 2 or of MoSiN having a nitrogencontent of 13 atom % (Mo:Si:N=1:3:0.6 in atomic ratio, thickness 23 nm)in Example 3. These photomask blanks were processed in accordance withphotomask manufacturing process A, whereby Levenson masks were produced.Sufficient resistance to oxygen-containing chlorine dry etching wasconfirmed. In the course of processing the blank of Example 2, anintermediate sample was obtained by stripping the resist film from theworkpiece at the stage when the ARF and light-shielding film werepatterned using the resist pattern, and the etch stop film was etched.This intermediate sample was sectioned and observed under a microscope.FIG. 16 is a photomicrograph of this light-shielding pattern section.FIG. 16 is a section of a film pattern (pattern width 0.2 μm) havingetch stop film 9, light-shielding film 2 of MoSiN, and ARF 3 of MoSiNdeposited on a transparent substrate 1 in the described sequence. Asseen from the photo, the film pattern is very good in perpendicularity.

Example 4 and Comparative Example

A photomask blank having the layer arrangement shown in FIG. 1B wasprepared by depositing the films by sputtering. The respective films areas follows.

-   Transparent substrate: quartz substrate-   Halftone phase shift film: MoSiON (Mo:Si:O:N=1:4:1:4 in atomic    ratio, thickness 75 nm)-   Etch stop film: CrN (Cr:N=9:1 in atomic ratio, thickness 10 nm)-   Light-shielding film: MoSiN (Mo:Si:N=1:3:1.5 in atomic ratio,    thickness 23 nm)-   ARF: MoSiN (thickness-wise compositional grading from    Mo:Si:N=1:3:1.5 in atomic ratio on light-shielding film side to    Mo:Si:N=1:5:5 in atomic ratio on side remote from transparent    substrate (surface side), thickness 18 nm)

For comparison purposes, a photomask blank was prepared in which thelight-shielding film was formed solely of prior art chromium-basedmaterial. The photomask blank of Comparative Example is a blankcomprising a light-shielding film and an ARF both of chromium-basedmaterial, and a halftone phase shift film of MoSiON as currentlycommonly used as the photomask blank for ArF lithography mask.

Specifically, a photomask blank as shown in FIG. 18 was prepared. On atransparent substrate 1, a MoSiON film (Mo:Si:O:N=1:4:1:4, thickness 75nm) as a halftone phase shift film 8, a CrN film (Cr:N=9:1, thickness 26nm) as a light-shielding film 23, and a CrON film (Cr:O:N=4:5:1,thickness 20 nm) as an ARF 5 were formed in sequence by sputtering.

These photomask blanks were evaluated for global loading and CDlinearity.

For global loading evaluation, a photomask was prepared as follows.First, a photosensitive resist (IP3500 by Tokyo Ohka Kogyo Co., Ltd.)was coated by means of a spin coater, and heated for baking. At thispoint, the resist film had a thickness of about 450 nm, as measured by aprobe type film gauge. The resist film was written imagewise by means ofa laser lithography system ALTA 3700 (Applied Material Inc.) anddeveloped, forming a test pattern. The test pattern has patternsincluding spaces with a size 1.0 μm arranged at total 121 (=11×11)points in a 132 mm square region on a 6-inch square substrate. Incertain zones, portions (dark portions) having a low write densityproximate to the pattern and a relatively small etched area areprovided. In the remaining zones, portions (clear portions) having ahigh write density proximate to the pattern and a relatively largeetched area are provided. Thereafter, each of the photomask blanks ofExample and Comparative Example was dry etched and processed throughconsecutive steps until halftone phase shift masks were completed. Thenthe pattern size was measured using a measurement tool LWM (Leica).

The halftone phase shift mask using Cr-based light-shielding film ofComparative Example showed a global loading tendency that the clearportions had a noticeably large space size than the dark portions. Incontrast, the halftone phase shift mask produced from the photomaskblank of Example showed a minimized global loading effect. Specifically,the difference in average values between the dark portion size and theclear portion size was about 15 nm in the halftone phase shift mask ofComparative Example, but was about 1 nm in the halftone phase shift maskproduced from the photomask blank of Example, demonstrating an apparenteffect.

For CD linearity evaluation, a photomask was produced as follows. Anegative chemically amplified EB resist was coated on the photomaskblank by means of a spin coater and baked to form a resist film of 200nm thick. This was followed by a series of steps including EB writing,PEB, development, and dry etching, completing a halftone phase shiftmask. The line width was measured by a SEM line width measuring system.

The data of linearity are plotted in the graph of FIG. 17. FIG. 17 showsthe results of measurement on the lines of a line-and-space patternhaving a line density of 50%. The halftone phase shift mask ofComparative Example shows the tendency that dry etching amenabilitybecomes worse as the line width becomes narrower. That is, as the designCD (on the abscissa) becomes smaller, an offset of line width from thedesign CD (ΔCD on the ordinate) becomes larger. In contrast, thehalftone phase shift mask of Example shows a dramatic decline of thetendency, i.e., excellent patterning characteristics.

It is seen from FIG. 17 that, as compared with Comparative Example(prior art), Example (the invention) is somewhat superior at a linewidth equal to or less than 0.8 μm and superior at a line width equal toor less than 0.4 μm. Then the photomask blank of the invention iseffective in producing a photomask having a pattern with a feature sizeequal to or less than 0.8 μm and most effective in producing a photomaskhaving a pattern with a feature size equal to or less than 0.4 μm.

Example 5

A photomask blank having the layer arrangement shown in FIG. 2A wasprepared by depositing the films by sputtering. The respective films areas follows.

-   Transparent substrate: quartz substrate-   Etch stop film: CrN (Cr:N=9:1 in atomic ratio, thickness 10 nm)-   Light-shielding film: MoSiN (Mo:Si:N=1:3:1.5 in atomic ratio,    thickness 41 nm)-   ARF: MoSiN (thickness-wise compositional grading from    Mo:Si:N=1:3:1.5 in atomic ratio on light-shielding film side to    Mo:Si:N=1:5:5 in atomic ratio on side remote from transparent    substrate (etching mask film side), thickness 18 nm)-   Etching mask film: CrN (Cr:N=9:1 in atomic ratio, thickness 10 nm)

This photomask blank was processed in accordance with photomaskmanufacturing process C, whereby a Levenson mask was produced. For thefirst and second resist films, a chemically amplified negative resistmainly comprising a hydroxystyrene resin, a crosslinker, and a photoacidgenerator was used to form a resist film of 250 nm thick. The resistfilms were patterned by EB lithography. The phase shifter formed in thetransparent substrate had a depth of 172 nm, which produces a phaseshift of about 180°.

As a result, a photomask which faithfully reflected the preselectedpattern size was produced independent of pattern density. It wasdemonstrated that the photomask blank has minimal pattern densitydependency. Since no erosion occurred on the substrate during etching ofthe light-shielding film, a phase shifter having the predetermined valueof phase shift could be formed in the substrate at a high accuracy.

Example 6

A photomask blank having the layer arrangement shown in FIG. 2A wasprepared by depositing the films by sputtering. The respective films areas follows.

-   Transparent substrate: quartz substrate-   Etch stop film: CrN (Cr:N=9:1 in atomic ratio, thickness 10 nm)-   Light-shielding film: MoSiN (Mo:Si:N=1:3:1.5 in atomic ratio,    thickness 41 nm)-   ARF: MoSiN (thickness-wise compositional grading from    Mo:Si:N=1:3:1.5 in atomic ratio on light-shielding film side to    Mo:Si:N=1:5:5 in atomic ratio on side remote from transparent    substrate (etching mask film side), thickness 18 nm)-   Etching mask film: CrN (Cr:N=9:1 in atomic ratio, thickness 10 nm)

This photomask blank was processed in accordance with photomaskmanufacturing process D, whereby a zebra type chromeless mask wasproduced. For the first and second resist films, a chemically amplifiednegative resist mainly comprising a hydroxystyrene resin, a crosslinker,and a photoacid generator was used to form a resist film of 200 nmthick. The resist films were patterned by EB lithography. The phaseshifter formed in the transparent substrate had a depth of 172 nm, whichproduces a phase shift of about 180°.

As a result, a photomask which faithfully reflected the preselectedpattern size was produced independent of pattern density. It wasdemonstrated that the photomask blank has minimal pattern densitydependency. Since no erosion occurred on the substrate during etching ofthe light-shielding film, a phase shifter having the predetermined valueof phase shift could be formed in the substrate at a high accuracy.

Example 7

A photomask blank having the layer arrangement shown in FIG. 2B wasprepared by depositing the films by sputtering. The respective films areas follows.

-   Transparent substrate: quartz substrate-   Halftone phase shift film: MoSiON (Mo:Si:O:N=1:4:1:4 in atomic    ratio, thickness 75 nm)-   Etch stop film: CrN (Cr:N=9:1 in atomic ratio, thickness 10 nm)-   Light-shielding film: MoSiN (Mo:Si:N=1:3:1.5 in atomic ratio,    thickness 41 nm)-   ARF: MoSiN (thickness-wise compositional grading from    Mo:Si:N=1:3:1.5 in atomic ratio on light-shielding film side to    Mo:Si:N=1:5:5 in atomic ratio on side remote from transparent    substrate (etching mask film side), thickness 18 nm)-   Etching mask film: CrN (Cr:N=4:1 in atomic ratio, thickness 10 nm)

This photomask blank was processed in accordance with photomaskmanufacturing process E, whereby a tritone phase shift mask wasproduced. For the first and second resist films, a chemically amplifiednegative resist mainly comprising a hydroxystyrene resin, a crosslinker,and a photoacid generator was used to form a resist film of 250 nmthick. The resist films were patterned by EB lithography.

As a result, a photomask which faithfully reflected the preselectedpattern size was produced independent of pattern density. It wasdemonstrated that the photomask blank has minimal pattern densitydependency. Since no erosion occurred on the phase shift film andsubstrate during etching of the light-shielding film, a phase shifterhaving the predetermined value of phase shift could be formed in thesubstrate at a high accuracy.

Example 8

A photomask blank having the layer arrangement shown in FIG. 3A wasprepared by depositing the films by sputtering. The respective films areas follows.

-   Transparent substrate: quartz substrate-   Etch stop film: CrN (Cr:N=9:1 in atomic ratio, thickness 10 nm)-   Light-shielding film: MoSiN (Mo:Si:N=1:3:1.5 in atomic ratio,    thickness 41 nm)-   1st ARF: MoSiN (thickness-wise compositional grading from    Mo:Si:N=1:3:1.5 in atomic ratio on light-shielding film side to    Mo:Si:N=1:5:5 in atomic ratio on side remote from transparent    substrate (2nd ARF side), thickness 10 nm)-   2nd ARF: CrON (Cr:O:N=4:5:1 in atomic ratio, thickness 8 nm)

This photomask blank was processed in accordance with photomaskmanufacturing process F, whereby a Levenson mask was produced. For thefirst and second resist films, a chemically amplified negative resistmainly comprising a hydroxystyrene resin, a crosslinker, and a photoacidgenerator was used to form a resist film of 200 nm thick. The resistfilms were patterned by EB lithography. The phase shifter formed in thetransparent substrate had a depth of 172 nm, which produces a phaseshift of about 180°.

As a result, a photomask which faithfully reflected the preselectedpattern size was produced independent of pattern density. It wasdemonstrated that the photomask blank has minimal pattern densitydependency. Since no erosion occurred on the substrate during etching ofthe light-shielding film, a phase shifter having the predetermined valueof phase shift could be formed in the substrate at a high accuracy.

Example 9

A photomask blank having the layer arrangement shown in FIG. 3B wasprepared by depositing the films by sputtering. The respective films areas follows.

-   Transparent substrate: quartz substrate-   Halftone phase shift film: MoSiON (No:Si:O:N=1:4:1:4 in atomic    ratio, thickness 75 nm)-   Etch stop film: CrN (Cr:N=9:1 in atomic ratio, thickness 10 nm)-   Light-shielding film: MoSiN (Mo:Si:N=1:3:1.5 in atomic ratio,    thickness 23 nm)-   1st ARF: MoSiN (thickness-wise compositional grading from    Mo:Si:N=1:3:1.5 in atomic ratio on light-shielding film side to    Mo:Si:N=1:5:5 in atomic ratio on side remote from transparent    substrate (2nd ARF side), thickness 10 nm)-   2nd ARF: CrON (Cr:O:N=4:5:1 in atomic ratio, thickness 8 nm)

This photomask blank was processed in accordance with photomaskmanufacturing process G, whereby a tritone phase shift mask wasproduced. For the first and second resist films, a chemically amplifiednegative resist mainly comprising a hydroxystyrene resin, a crosslinker,and a photoacid generator was used to form a resist film of 100 nmthick. The resist films were patterned by EB lithography.

As a result, a photomask which faithfully reflected the preselectedpattern size was produced independent of pattern density. It wasdemonstrated that the photomask blank has minimal pattern densitydependency. Since no erosion occurred on the phase shift film andsubstrate during etching of the light-shielding film, a phase shifterhaving the predetermined value of phase shift could be formed in thesubstrate at a high accuracy.

Example 10

A photomask blank having the layer arrangement shown in FIG. 4B wasprepared by depositing the films by sputtering. The respective films areas follows.

-   Transparent substrate: quartz substrate-   Halftone phase shift film: MoSiON (Mo:Si:O:N=1:4:1:4 in atomic    ratio, thickness 75 nm)-   Etch stop film: CrN (Cr:N=9:1 in atomic ratio, thickness 10 nm)-   Light-shielding film: MoSiN (Mo:Si:N=1:3:1.5 in atomic ratio,    thickness 23 nm)-   ARF: CrON (Cr:O:N=4:5:1 in atomic ratio, thickness 18 nm)

This photomask blank was processed in accordance with photomaskmanufacturing process H, whereby a halftone phase shift mask wasproduced. For the first and second resist films, a chemically amplifiednegative resist mainly comprising a hydroxystyrene resin, a crosslinker,and a photoacid generator was used to form a resist film of 100 nmthick. The resist films were patterned by EB lithography.

As a result, a photomask which faithfully reflected the preselectedpattern size was produced independent of pattern density. It wasdemonstrated that the photomask blank has minimal pattern densitydependency. Since no erosion occurred on the phase shift film andsubstrate during etching of the light-shielding film, a phase shifterhaving the predetermined value of phase shift could be formed in thesubstrate at a high accuracy.

Example 11

A photomask blank having the layer arrangement shown in FIG. 5B wasprepared by depositing the films by sputtering. The respective films areas follows.

-   Transparent substrate: quartz substrate-   Halftone phase shift film: MoSiON (Mo:Si:O:N=1:4:1:4 in atomic    ratio, thickness 75 nm)-   Etch stop film: CrN (Cr:N=9:1 in atomic ratio, thickness 10 nm)-   1st light-shielding layer: MoSiN (Mo:Si:N=1:3:1.5 in atomic ratio,    thickness 20 nm)-   2nd light-shielding layer: CrN (Cr:N=4:1 in atomic ratio, thickness    5 nm)-   ARF: CrON (Cr:O:N=4:5:1 in atomic ratio, thickness 20 nm)

This photomask blank was processed in accordance with photomaskmanufacturing process I, whereby a halftone phase shift mask wasproduced. For the first and second resist films, a chemically amplifiednegative resist mainly comprising a hydroxystyrene resin, a crosslinker,and a photoacid generator was used to form a resist film of 250 nmthick. The resist films were patterned by EB lithography.

As a result, a photomask which faithfully reflected the preselectedpattern size was produced independent of pattern density. It wasdemonstrated that the photomask blank has minimal pattern densitydependency. Since no erosion occurred on the phase shift film andsubstrate during etching of the light-shielding film, a phase shifterhaving the predetermined value of phase shift could be formed in thesubstrate at a high accuracy.

Japanese Patent Application No. 2006-065800 is incorporated herein byreference.

Although some preferred embodiments have been described, manymodifications and variations may be made thereto in light of the aboveteachings. It is therefore to be understood that the invention may bepracticed otherwise than as specifically described without departingfrom the scope of the appended claims.

1. A photomask comprising a transparent substrate and a mask patternformed thereon, said mask pattern comprising transparent regions, phaseshift regions and light-shielding regions, and said mask patterncomprising an etch stop film disposed on the substrate with another filmintervening therebetween, said etch stop film of single layer ormultilayer construction being resistant to fluorine dry etching andremovable by chlorine dry etching, said another film comprising ahalftone phase shift film, a light-shielding film disposed contiguous tosaid etch stop film and consisting of a single layer or multiple layerscomposed of a material containing a transition metal and silicon, and anantireflective film disposed contiguous to said light-shielding film andconsisting of a single layer or multiple layers, wherein said transitionmetal is at least one element selected from the group consisting oftitanium, vanadium, cobalt, nickel, zirconium, niobium, molybdenum,hafnium, tantalum, and tungsten, and an optical density OD of thecombination of phase shift film, etch stop film, light-shielding filmand antireflective film is at least 2.5.
 2. The photomask of claim 1,wherein said etch stop film is composed of chromium alone or a chromiumcompound containing chromium and at least one element selected fromoxygen, nitrogen and carbon.
 3. The photomask of claim 1, wherein saidetch stop film is composed of tantalum alone or a tantalum compoundcontaining tantalum and free of silicon.
 4. The photomask of claim 1,wherein said etch stop film has a thickness of 2 to 20 nm.
 5. Thephotomask of claim 1, wherein the material of which the layer of saidlight-shielding film is composed is an alloy of a transition metal withsilicon or a transition metal silicon compound containing a transitionmetal, silicon and at least one element selected from oxygen, nitrogenand carbon.
 6. The photomask of claim 1, wherein the material of whichthe layer of said light-shielding film is composed is a transition metalsilicon compound containing a transition metal, silicon and nitrogen. 7.The photomask of claim 6, wherein said light-shielding film has anitrogen content of 5 atom % to 40 atom %.
 8. The photomask of claim 1,wherein said light-shielding film consists of multiple layers, amongwhich a layer disposed contiguous to said antireflective film has anextinction coefficient k of at least 1.5 relative to exposure light. 9.The photomask of claim 1, wherein said light-shielding film has athickness of 10 to 80 nm.
 10. The photomask of claim 1, wherein saidantireflective film includes a layer of a transition metal siliconcompound containing a transition metal, silicon, and oxygen and/ornitrogen.
 11. The photomask of claim 1, wherein said antireflective filmincludes a layer of chromium alone or chromium compound containingchromium and oxygen and/or nitrogen.
 12. The photomask of claim 1,wherein said antireflective film consists of two layers, a firstantireflective layer formed adjacent to the transparent substrate and asecond antireflective layer formed remote from the transparentsubstrate, the first antireflective layer is composed of a transitionmetal silicon compound comprising a transition metal, silicon and oxygenand/or nitrogen, and the second antireflective layer is composed of achromium compound containing chromium and oxygen and/or nitrogen. 13.The photomask of claim 11, wherein said antireflective film, the layerof chromium compound has a chromium content of at least 50 atom %. 14.The photomask of claim 1, further comprising an etching mask filmdisposed contiguous to said antireflective film and consisting of asingle layer or multiple layers which are resistant to fluorine dryetching and removable by chlorine dry etching.
 15. The photomask ofclaim 14, wherein said etching mask film is composed of chromium aloneor a chromium compound containing chromium and at least one elementselected from oxygen, nitrogen and carbon.
 16. The photomask of claim14, wherein said etching mask film has a thickness of 2 to 30 nm. 17.The photomask of claim 10, wherein said transition metal of saidantireflective film is at least one element selected from the groupconsisting of titanium, vanadium, cobalt, nickel, zirconium, niobium,molybdenum, hafnium, tantalum, and tungsten.
 18. The photomask of claim1, wherein said transition metal is molybdenum.
 19. The manufacturingprocess of a photomask of claim 1, said photomask being a tritone phaseshift mask, said process comprising steps of: providing a photomaskblank comprising a transparent substrate, an etch stop film disposed onthe substrate with another film intervening therebetween, said etch stopfilm of single layer or multilayer construction being resistant tofluorine dry etching and removable by chlorine dry etching, said anotherfilm comprising a halftone phase shift film, a light-shielding filmdisposed contiguous to said etch stop film and consisting of a singlelayer or multiple layers composed of a material containing a transitionmetal and silicon, and an antireflective film disposed contiguous tosaid light-shielding film and consisting of a single layer or multiplelayers, wherein said transition metal is at least one element selectedfrom the group consisting of titanium, vanadium, cobalt, nickel,zirconium, niobium, molybdenum, hafnium, tantalum, and tungsten, and anoptical density OD of the combination of phase shift film, etch stopfilm, light-shielding film and antireflective film is at least 2.5;coating a first resist film onto the blank; processing the first resistfilm to form a pattern corresponding to the configuration of a portionof the halftone phase shift film to be left; transferring the pattern offirst resist film to the antireflective film and light-shielding film byfluorine dry etching; etching the etch stop film by chlorine dry etchingto form an opening at the area where halftone phase shift film is to beremoved; stripping the first resist film: coating a second resist film;processing the second resist film into a pattern corresponding to theconfiguration of a portion of light-shielding film is to be left, forprotecting the light-shielding film and antireflective film: removing aportion of the halftone phase shift film in register with the opening inthe etch stop film, and portions of the antireflective film andlight-shielding film which are not protected by the second resist film,by fluorine dry etching and; etching a portion of the etch stop filmwhich is not protected by the second resist film, by chlorine dryetching.
 20. A manufacturing process of a photomask of claim 1, saidphotomask being a tritone phase shift mask, said process comprisingsteps of: providing a photomask blank comprising a transparentsubstrate, an etch stop film disposed on the substrate with another filmintervening therebetween, said etch stop film of single layer ormultilayer construction being resistant to fluorine dry etching andremovable by chlorine dry etching, said another film comprising ahalftone phase shift film, a light-shielding film disposed contiguous tosaid etch stop film and consisting of a single layer or multiple layerscomposed of a material containing a transition metal and silicon, anantireflective film disposed contiguous to said light-shielding film andconsisting of a single layer or multiple layers, and an etching maskfilm disposed contiguous to said antireflective film and consisting of asingle layer or multiple layers which are resistant to fluorine dryetching and removable by chlorine dry etching, wherein said transitionmetal is at least one element selected from the group consisting oftitanium, vanadium, cobalt, nickel, zirconium, niobium, molybdenum,hafnium, tantalum, and tungsten, and an optical density OD of thecombination of phase shift film, etch stop film, light-shielding filmand antireflective film is at least 2.5; coating a first resist filmonto the blank; processing the first resist film to form a patterncorresponding to the configuration of a portion of the halftone phaseshift film to be left; transferring the pattern of first resist film tothe etching mask film by chlorine dry etching; transferring the patternof etching mask film to the antireflective film and light-shielding filmby fluorine dry etching; stripping the first resist film; coating asecond resist film; processing the second resist film into a patterncorresponding to the configuration of a portion of light-shielding filmto be left, for protecting the area of etching mask film wherelight-shielding film is to be left; etching the etch stop film to forman opening at the area where halftone phase shift film is to be removed,and the etching mask film in the area where light-shielding film is tobe removed, by chlorine dry etching; removing a portion of the halftonephase shift film in register with the opening in the etch stop film, andportions of the antireflective film and light-shielding film which arenot protected by the etching mask film, by fluorine dry etching;stripping the second resist film; and removing a portion of etch stopfilm which is left in the area where light-shielding film is to beremoved, and a portion of etching mask film overlying the antireflectivefilm on the unremoved light-shielding film, by chlorine dry etching. 21.A manufacturing process of a photomask of claim 1, said photomask beinga tritone phase shift mask, said process comprising steps of: providinga photomask blank comprising a transparent substrate, an etch stop filmdisposed on the substrate with another film intervening therebetween,said etch stop film of single layer or multilayer construction beingresistant to fluorine dry etching and removable by chlorine dry etching,said another film comprising a halftone phase shift film, alight-shielding film disposed contiguous to said etch stop film andconsisting of a single layer or multiple layers composed of a materialcontaining a transition metal and silicon, and an antireflective filmdisposed contiguous to said light-shielding film and consisting of asingle layer or multiple layers, wherein said antireflective filmconsists of two layers, a first antireflective layer formed adjacent tothe transparent substrate and a second antireflective layer formedremote from the transparent substrate, the first antireflective layer issusceptible to fluorine dry etching, and the second antireflective layeris resistant to fluorine dry etching, said transition metal is at leastone element selected from the group consisting of titanium, vanadium,cobalt, nickel, zirconium, niobium, molybdenum, hafnium, tantalum, andtungsten, and an optical density OD of the combination of phase shiftfilm, etch stop film, light-shielding film and antireflective film is atleast 2.5; coating a first resist film onto the blank; processing thefirst resist film to form a pattern corresponding to the configurationof a portion of the halftone phase shift film to be left; transferringthe pattern of first resist film to the second antireflective layer bychlorine dry etching: transferring the pattern of second antireflectivelayer to the first antireflective layer and light-shielding film byfluorine dry etching; stripping the first resist film; coating a secondresist film; processing the second resist film into a patterncorresponding to the configuration of a portion of light-shielding filmto be left, for protecting the area of second antireflective layer wherelight-shielding film is to be left; etching the etch stop film bychlorine dry etching to form an opening at the area where halftone phaseshift film is to be removed, and the second antireflective layer in thearea where light-shielding film is to be removed; removing a portion ofthe halftone phase Shift film in register with the opening in the etchstop film, and portions of the first antireflective layer andlight-shielding film which are not protected by the secondantireflective layer, by fluorine dry etching; removing a portion ofetch stop film which is left in the area where light-shielding film isto be removed by chlorine dry etching; and stripping the second resistfilm.
 22. A manufacturing process of a photomask of claim 1, saidphotomask being a halftone phase shift mask, said process comprisingsteps of: providing a photomask blank comprising a transparentsubstrate, an etch stop film disposed on the substrate with another filmintervening therebetween, said etch stop film of single layer ormultilayer construction being resistant to fluorine dry etching andremovable by chlorine dry etching, said another film comprising ahalftone phase shift film, a light-shielding film disposed contiguous tosaid etch stop film and consisting of a single layer or multiple layerscomposed of a material containing a transition metal and silicon, and anantireflective film disposed contiguous to said light-shielding film andconsisting of a single layer or multiple layers, wherein said transitionmetal is at least one element selected from the group consisting oftitanium, vanadium, cobalt, nickel, zirconium, niobium, molybdenum,hafnium, tantalum, and tungsten, and an optical density OD of thecombination of phase shift film, etch stop film, light-shielding filmand antireflective film is at least 2.5; coating a first resist filmonto the blank; processing the first resist film to form a patterncorresponding to the configuration of a portion of the halftone phaseshift film to be left; transferring the pattern of first resist film tothe antireflective film by chlorine dry etching; transferring thepattern of antireflective film to the light-shielding film by fluorinedry etching; stripping the first resist film; coating a second resistfilm; processing the second resist film into a pattern corresponding tothe configuration of a portion of light-shielding film to be left, forprotecting the area of antireflective film where light-shielding film isto be left; etching the etch stop film to form an opening at the areawhere halftone phase shift film is to be removed, and the antireflectivefilm which is not protected by the second resist film, by chlorine dryetching; removing a portion of the halftone phase shift film in registerwith the opening in the etch stop film, and a portion of thelight-shielding film which is exposed after removal of antireflectivefilm, by fluorine dry etching; removing a portion of etch stop filmwhich is exposed after removal of light-shielding film by chlorine dryetching; and stripping the second resist film.
 23. A manufacturingprocess of a photomask of claim 1, said photomask being a halftone phaseshift mask, said process comprising steps of: providing a photomaskblank comprising a transparent substrate, an etch stop film disposed onthe substrate with another film intervening therebetween, said etch stopfilm of single layer or multilayer construction being resistant tofluorine dry etching and removable by chlorine dry etching, said anotherfilm comprising a halftone phase shift film, a light-shielding filmdisposed contiguous to said etch stop film and consisting of a singlelayer or multiple layers composed of a material containing a transitionmetal and silicon, and an antireflective film disposed contiguous tosaid light-shielding film and consisting of a single layer or multiplelayers, wherein said light-shielding film consists of two layers, afirst light-shielding layer formed adjacent to the transparent substrateand a second light-shielding layer formed remote from the transparentsubstrate, the first light-shielding layer is susceptible to fluorinedry etching, and the second light-shielding layer is resistant tofluorine dry etching, said transition metal is at least one elementselected from the group consisting of titanium, vanadium, cobalt,nickel, zirconium, niobium, molybdenum, hafnium, tantalum, and tungsten,and an optical density OD of the combination of phase shift film, etchstop film, light-shielding film and antireflective film is at least 2.5;coating a first resist film onto the blank; processing the first resistfilm to form a pattern corresponding to the configuration of a portionof the halftone phase shift film to be left; transferring the pattern offirst resist film to the antireflective layer and second light-shieldinglayer by chlorine dry etching; transferring the pattern ofantireflective layer and second light-shielding layer to the firstlight-shielding layer by fluorine dry etching; stripping the firstresist film; coating a second resist film; processing the second resistfilm into a pattern corresponding to the configuration of a portion oflight-shielding film to be left, for protecting the area ofantireflective film where light-shielding film is to be left; etchingthe etch stop film by chlorine dry etching to form an opening at thearea where halftone phase shift film is to be removed, and theantireflective film and second light-shielding layer in the area wherelight-shielding film is to be removed; removing a portion of thehalftone phase shift film in register with the opening in the etch stopfilm, and a portion of the first light-shielding layer which is notprotected by the antireflective film and second light-shielding layer,by fluorine dry etching; removing a portion of etch stop film which isleft in the area where light-shielding film is to be removed by chlorinedry etching; and stripping the second resist film.